Preoperative localization procedures for initial surgery in primary hyperparathyroidism

The experience of the surgeon and precise localization of abnormal parathyroid glands determine the success of surgery for primary hyperparathyroidism (HPT). In HPT patients undergoing repeat surgery, the use of localization studies improved the ability to identify the remaining abnormal parathyroid tissue. This study investigated the roles of preoperative localization techniques for initial surgery for primary HPT. From 1985 through 1997, two noninvasive localization procedures, ultrasonography (US) and 201thallium chloride-99mtechnetium pertechnetate subtraction scanning (Tl-Tc), were used prior to initial exploration for primary HPT in 76 patients. Their accuracy was determined on the basis of surgical and pathologic results. The surgical success rate was 96% (73/76). The sensitivities of US and Tl-Tc were 71% and 49%, respectively. The sensitivity of Tl-Tc was higher for the lower parathyroid glands. In 21 of 26 patients who underwent fine-needle aspiration (FNA) of the suspected enlarged parathyroid gland, the diagnosis of parathyroid adenoma was confirmed preoperatively. We conclude that the concomitant use of US and FNA is a safe and convenient method for preoperative localization of the parathyroid glands prior to initial surgical exploration in patients with primary HPT. Bilateral neck exploration by an experienced surgeon should be the routine procedure. US and Tl-Tc alone offer limited localization information, and unilateral exploration should be reserved for selected cases in which the results of these two imaging studies are consistent with one another.

Metabolism of 2',3'-dideoxy-2',3'-didehydro-beta-L(-)-5-fluorocytidine and its activity in combination with clinically approved anti-human immunodeficiency virus beta-D(+) nucleoside analogs in vitro

2',3'-Dideoxy-2',3'-didehydro-beta-L(-)-5-fluorocytidine [L(-)Fd4C] has been reported to be a potent inhibitor of the human immunodeficiency virus (HIV) in cell culture. In the present study the antiviral activity of this compound in two-drug combinations and its intracellular metabolism are addressed. The two-drug combination of L(-)Fd4C plus 2',3'-didehydro-2'-3'-dideoxythymidine (D4T, or stavudine) or 3'-azido-3'-deoxythymidine (AZT, or zidovudine) synergistically inhibited replication of HIV in vitro. Additive antiviral activity was observed with L(-)Fd4C in combination with 2',3'-dideoxycytidine (ddC, or zalcitabine) or 2',3'-dideoxyinosine (ddI, or didanosine). This beta-L(-) nucleoside analog has no activity against mitochondrial DNA synthesis at concentrations up to 10 microM. As we previously reported for other beta-L(-) nucleoside analogs, L(-)Fd4C could protect against mitochondrial toxicity associated with D4T, ddC, and ddI. Metabolism studies showed that this drug is converted intracellularly to its mono-, di-, and triphosphate metabolites. The enzyme responsible for monophosphate formation was identified as cytoplasmic deoxycytidine kinase, and the K(m) is 100 microM. L(-)Fd4C was not recognized in vitro by human mitochondrial deoxypyrimidine nucleoside kinase. Also, L(-)Fd4C was not a substrate for deoxycytidine deaminase. L(-)Fd4C 5'-triphosphate served as an alternative substrate to dCTP for incorporation into DNA by HIV reverse transcriptase. The favorable anti-HIV activity and protection from mitochondrial toxicity by L(-)Fd4C in two-drug combinations favors the further development of L(-)Fd4C as an anti-HIV agent.

(Z)- and (E)-2-(hydroxymethylcyclopropylidene)-methylpurines and pyrimidines as antiviral agents

Several Z- and E-methylenecyclopropane nucleoside analogues were synthesized and tested for antiviral activity in vitro against human and murine cytomegalovirus (HCMV, MCMV), Epstein-Barr virus (EBV), varicella zoster virus (VZV), hepatitis B virus (HBV), herpes simplex virus types 1 and 2 (HSV-1, HSV-2), human herpesvirus 6 (HHV-6) and human immunodeficiency virus type 1 (HIV-1). The Z-2-amino-6-cyclopropylaminopurine analogue was the most effective agent against HCMV (EC50 or EC90 0.4-2 microM) followed by syncytol and the Z-2,6-diaminopurine analogues (EC50 or EC90 3.4-29 and 11-24 microM, respectively). The latter compound was also a strong inhibitor of MCMV (EC50 0.6 microM). Syncytol was the most potent against EBV (EC50 < 0.41 and 2.5 microM) followed by the Z-2,6-diaminopurine (EC50 1.5 and 6.9 microM) and the Z-2-amino-6-cyclopropyl-aminopurine derivative (EC50 11.8 microM). Syncytol was also most effective against VZV (EC50 3.6 microM). Activity against HSV-1, HSV-2 and HHV-6 was generally lower; synthymol had an EC50 of 2 microM against HSV-1 (ELISA) and 1.3 microM against EBV in Daudi cells but was inactive in other assays. The 2-amino-6-cyclopropylamino analogue displayed EC50 values between 215 and > 74 microM in HSV-1 and HSV-2 assays. 2-Amino-6-cyclopropylaminopurine and 2,6-diaminopurine derivatives were effective against HBV (EC50 2 and 10 microM, respectively), whereas none of the analogues inhibited HIV-1 at a higher virus load. Syncytol and the E isomer were equipotent against EBV in Daudi cells but the E isomer was much less effective in DNA hybridization assays. The E-2,6-diaminopurine analogue and E isomer of synthymol were devoid of antiviral activity.

Anti-hepatitis B virus activity and metabolism of 2',3'-dideoxy-2',3'-didehydro-beta-L(-)-5-fluorocytidine

2',3'-Dideoxy-2',3'-didehydro-beta-L(-)-5-fluorocytidine [L(-)Fd4C] was found to be at least 10 times more potent than beta-L-2',3'-dideoxy-3'-thiacytidine [L(-)SddC; also called 3TC, or lamivudine]against hepatitis B virus (HBV) in culture. Its cytotoxicity against HepG2 growth in culture was also greater than that of L(-)SddC (3TC). There was no activity of this compound against mitochondrial DNA synthesis in cells at concentrations upto 10 microM. The dynamics of recovery of virus from the medium of cells pretreated with equal drug concentrations were slower with L(-)Fd4C than with L(-)SddC (3TC). L(-)Fd4C could be metabolized to mono-, di-, and triphosphate forms. The degree of L(-)Fd4C phosphorylation to the 5'-triphosphate metabolite was higher than the degree of L(-)SddC (3TC) phosphorylation when equal extracellular concentrations of the two drugs were used. The apparent K(m) of L(-)Fd4C phosphorylated metabolites formed intracellularly was higher than that for L(-)SddC (3TC). This may be due in part to a difference in the behavior of L(-)Fd4C and L(-)SddC (3TC) towards cytosolic deoxycytidine kinase. Furthermore, L(-)Fd4C 5'-triphosphate was retained longer within cells than L(-)SddC (3TC) 5-triphosphate. L(-)Fd4C 5'-triphosphate inhibited HBV DNA polymerase in competition with dCTP with a Ki of 0.069 +/- 0.015 microM. Given the antiviral potency and unique pharmacodynamic properties of L(-)Fd4C, this compound should be considered for development as an expanded-spectrum anti-HBV drug.

Biochemical characterization of the HIV-1 integrase 3'-processing activity and its inhibition by phosphorothioate oligonucleotides

To better understand HIV-1 integrase (IN) functions, we determined the kinetic parameters of the 3'-processing reaction. Steady-state kinetic analysis performed using Dixon plots indicated that the concentration of active enzyme was 10-fold lower than that calculated by protein determination. The turnover number was low, suggesting that IN remained bound to DNA after cleavage. The catalytic efficiency increased 10-fold from 30 to 37 degrees C and 2-fold from 37 to 42 degrees C. In enzyme assays carried out at 37 degrees C, both single- and double-stranded phosphorothioate oligos bound to IN with an efficiency comparable to that of the phosphodiester duplex substrate. The competition efficiency of single-stranded oligos was directly related to the sequence length. On the other hand, phosphorothioate duplex U5 LTRs modified in the plus strand were capable of both competing with the substrate and directly inhibiting the 3'-processing activity. These results suggest that, in addition to other modes of action (inhibition of gp120-CD4 interaction and reverse transcriptase), phosphorothioate hetero- and homopolimeric oligos also potently inhibit the IN activity.

Role of additional mutations outside the YMDD motif of hepatitis B virus polymerase in L(-)SddC (3TC) resistance

L(-)SddC (3TC) has been shown to be the most promising nucleoside analogue used for the treatment of hepatitis B virus (HBV) infection. Unfortunately, it has been reported that about 12% of HBV-infected patients experience a recurrence of HBV after a period of treatment with 3TC. Point mutations were detected in the HBV polymerase of those viruses from 3TC-resistant patients. A common mutation occurred at methionine in the YMDD motif. In this report, we present mutants that were generated from the HBV genome (adr subtype) by site-directed mutagenesis based on clinical reports from other investigators. With the transient transfection system, it was found that by changing methionine to valine or isoleucine at the YMDD motif, the viral DNA replication would be more than 100-fold less efficient than that of the wild-type virus. Some additional mutations outside the YMDD motif could enhance the replication of the virus containing a YMDD mutation. Various levels of resistance to 3TC were observed in HBV mutants containing point mutations both inside and outside the YMDD motif. These results suggest that the mutations outside the YMDD motif compensate the YMDD mutation to some extent for the viral replication and may also contribute to clinical viral resistance to 3TC.

Interaction of beta-L-2',3'-dideoxy-2',3'-didehydro-5-fluoro-CTP with human immunodeficiency virus-1 reverse transcriptase and human DNA polymerases: implications for human immunodeficiency virus drug design

The work reported in this article has evaluated the relative molecular activity of the 5'-triphosphate of a novel beta-L-nucleoside with an unsaturated ribose residue, beta-L-2', 3'-dideoxy-2',3'-didehydro-5-fluorocytidine (beta-L-Fd4CTP), with that of beta-L-2',3'-dideoxy-5-fluorocytidine (beta-L-FddCTP) and 2', 3'-dideoxycytidine (ddCTP), on DNA strand elongation by human immunodeficiency virus-1 reverse transcriptase (HIV RT) and human DNA polymerases alpha (pol alpha), beta (pol beta), gamma (pol gamma), and epsilon (pol epsilon). The concentrations of beta-L-Fd4CTP that inhibited the yield of products by 50% were 0.20 micro M, 1.8 micro M, and 4.0 micro M for HIV RT, pol gamma, and pol beta, respectively. The beta-L-Fd4CTP at a concentration as high as 40 micro M had no inhibitory effect on pol epsilon, but could inhibit pol alpha by 10-20% at 20 micro M. The Km and relative Vmax values of beta-L-Fd4CTP, beta-L-FddCTP, and ddCTP for incorporation into the standing start point of 5'-[32P]-oligonucleotide primer annealed with M13mp19 phage DNA by HIV RT and human DNA polymerases were evaluated. The efficiency of incorporation (Vmax/Km) of beta-L-Fd4CTP by HIV RT was about 4-fold and 12-fold higher than that of ddCTP and beta-L-FddCTP, respectively. In contrast, the Vmax/Km ratio of beta-L-Fd4CTP for pol gamma was 7-fold lower than that of ddCTP, but 4-fold higher than that of beta-L-FddCTP. Pol alpha could use beta-L-Fd4CTP as a substrate, but only at a high concentration (>20 micro M). Incorporation of beta-L-Fd4CTP by pol epsilon could not be detected. A hypothesis about the preferable recognition of the 2',3'-dideoxy-2',3'-didehydro- structure of beta-L-Fd4CTP to that of the 2',3'-dideoxy-structure of beta-L-FddCTP by HIV RT is discussed.

Telomerase from human leukemia cells: properties and its interaction with deoxynucleoside analogues

Telomerase is a unique reverse transcriptase involved in the maintenance of genomic integrity. In an attempt to understand the properties of this enzyme and to study the effect of deoxynucleoside analogues, we have isolated and partially purified telomerase from the blast cells of a patient with acute myelogenous leukemia. During the course of purification of telomerase, three characteristic forms of this enzyme activity were separated. Two processive forms and one less processive form were noted. All forms of the enzyme activities could be abolished by RNase A and proteinase K treatments, implying that they are ribonucleoproteins. The major form of telomerase was characterized with respect to divalent ion requirements, effect of salt and nonionic detergents. The Km of deoxynucleoside triphosphates was determined with a modified telomerase repeat array protocol assay. Studies with deoxynucleoside analogues indicated that 3'-azido-3'deoxythymidine triphosphate is much more inhibitory than 2',3'-dideoxy 2',3'didehydrothymidine triphosphate, and the cytidine analogue ddCTP was not inhibitory. ddGTP was the most potent inhibitor among all dideoxynucleosides studied.

Decreased drug accumulation without increased drug efflux in a novel MRP-overexpressing multidrug-resistant cell line

KB/7D cells represent a multidrug-resistant subclone of human nasopharyngeal carcinoma KB cells generated by continuous exposure to the topoisomerase II inhibitor VP-16 (etoposide). KB/7D cells also show cross-resistance to doxorubicin and vincristine. Phenotypic traits of the cell line include a 2-fold decrease in topoisomerase II levels and a decrease in the uptake of VP-16 without an increase in the rate of drug efflux or expression of P-glycoprotein, suggesting a novel mechanism associated with the uptake of anticancer drugs. This study demonstrated that the multidrug-resistance associated protein (MRP) is overexpressed in KB/7D cells, and that the loss of resistance in revertant cells correlates with the loss of MRP. The resistance to VP-16 and doxorubicin could be overcome, partially, and resistance to vincristine could be overcome completely, by the L-enantiomer of verapamil, but not by the D-enantiomer or by BIBW 22 (4-[N-(2-hydroxy-2-methyl-propyl)-ethanolamino]-2,7-bis[cis-2,6-++ +dimethylmorpholino)-6-phenylpteridin), an inhibitor of MDR-1. L-Verapamil was shown to be significantly more potent than D-verapamil in modulating the accumulation defect in KB/7D cells towards doxorubicin, as measured by flow cytometry and confocal microscopy, and towards VP-16, as measured by increases in protein-linked DNA strand breaks. This suggests that KB/7D cells are multidrug resistant due to decreases in topoisomerase II levels and the overexpression of MRP, that MRP leads to a decrease in drug accumulation, and that L-verapamil can modulate the MRP-associated accumulation defect and drug-resistance phenotype. This contrasts with previous studies that suggest that MRP causes multidrug resistance by exporting cytotoxic drugs out of the cell and that did not show modulation of MRP by verapamil.

Interaction of human plasma membrane proteins and oligodeoxynucleotides

Two oligodeoxynucleotide (oligodN) binding proteins of 100-110 kDa on plasma membranes of human cell lines were recently identified by us. These two proteins seemed to play a role in oligodN uptake. In this study, the impact of the chain length and the sequence of the oligodN on the interaction with those two proteins was investigated. Chain length of oligodN was an important determinant, but not the sole determinant for the interaction. Binding affinity of oligodNs was determined predominantly by base composition, where pyrimidine bases but not purine bases were required in the sequence to retain high affinity. The binding kinetics of the homopolymers of deoxycytidine (dC21) and deoxythymidine (dT21) suggests that the proteins may have different binding sites, with one site preferring thymine bases and the other cytosine bases. Moreover, some additional plasma membrane proteins were identified, with an apparent molecular mass ranging from 40 to 58 kDa, which could bind thymine bases but not cytosine bases.

Unique inhibitory effect of 1-(2'-deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil 5'-triphosphate on Epstein-Barr virus and human DNA polymerases

1-(2'-Deoxy-2'-fluoro-beta-L-arabinofuranosyl)-5-methyluracil (L-FMAU) was shown to have potent antiviral activity against Epstein-Barr virus (EBV) without any cellular toxicity at concentrations up to 200 microM (Yao et al., Biochem Pharmacol 51: 941-947, 1996). The 5'-triphosphate of L-FMAU was not a substrate for EBV or cellular DNA polymerases, but could inhibit the elongation reaction, 3'-to-5' exonuclease activity, and nucleotide turnover catalyzed by EBV DNA polymerase. DNA synthesis catalyzed by human DNA polymerases was inhibited to a lesser extent. The inhibition pattern of EBV DNA polymerase by L-FMAU-5'-triphosphate (L-FMAU-TP) was consistent with an uncompetitive mechanism when dNTP or template-primer were used as the variable substrates. The Ki values were 38+/-10 microM for the elongation reaction, and about 50+/-10 microM for both nucleotide exchange and 3'-to-5' exonuclease reactions, values that were 10-20 times less than that for GMP. L-FMAU-TP is the first nucleoside 5'-triphosphate shown to have such unique behavior toward DNA polymerases. EBV DNA polymerase could be one of the targets for the inhibitory effect of L-FMAU-TP on EBV replication.

Unique metabolism of a novel antiviral L-nucleoside analog, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil: a substrate for both thymidine kinase and deoxycytidine kinase

2'-Fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU) is the first L-nucleoside analog with low cytotoxicity discovered to have potent antiviral activities against both hepatitis B virus and Epstein-Barr virus but not human immunodeficiency virus. This spectrum of activity is different from those of the other L-nucleoside analogs examined. L-FMAU enters cells through equilibrative-sensitive and -insensitive nucleoside transport as well as through nonfacilitated passive diffusion. L-FMAU is phosphorylated stepwise in cells to its mono-, di-, and triphosphate forms. In the present study the enzymes responsible for the first step of L-FMAU phosphorylation were identified. This is the first thymidine analog shown to be a substrate not only for cytosolic thymidine kinase and mitochondrial deoxypyrimidine kinase but also for deoxycytidine kinase. This finding suggests that the antiviral activity of L-FMAU will not be limited by the loss or alteration of any of these deoxynucleoside kinases.

Inhibitory effect of 2'-fluoro-5-methyl-beta-L-arabinofuranosyl-uracil on duck hepatitis B virus replication

The antiviral activity of 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU), a novel L-nucleoside analog of thymidine known to be an inhibitor of hepatitis B virus (HBV) replication in hepatoma cells (2.2.1.5 cell line), was evaluated in the duck HBV (DHBV) model. Short-term oral administration (5 days) of L-FMAU (40 mg/kg of body weight/day) to experimentally infected ducklings induced a significant decrease in the level of viremia. This antiviral effect was sustained in animals when therapy was prolonged for 8 days. The histological study showed no evidence of liver toxicity in the L-FMAU-treated group. By contrast, microvesicular steatosis was found in the livers of dideoxycytidine-treated animals. L-FMAU administration in primary duck hepatocyte cultures infected with DHBV induced a dose-dependent inhibition of both virion release in culture supernatants and intracellular viral DNA synthesis, without clearance of viral covalently closed circular DNA. By using a cell-free system for the expression of an enzymatically active DHBV reverse transcriptase, it was shown that L-FMAU triphosphate exhibits an inhibitory effect on the incorporation of dAMP in the viral DNA primer. Thus, our data demonstrate that L-FMAU inhibits DHBV replication in vitro and in vivo. Long-term administration of L-FMAU for the eradication of viral infection in animal models of HBV infection should be evaluated.

(Z)- and (E)-2-((hydroxymethyl)cyclopropylidene)methyladenine and -guanine. New nucleoside analogues with a broad-spectrum antiviral activity

New nucleoside analogues 14-17 based on a methylenecyclopropane structure were synthesized and evaluated for antiviral activity. Reaction of 2,3-dibromopropene (19) with adenine (18) led to bromoalkene 20, which was benzoylated to give N6,N6-dibenzoyl derivative 23. Attempts to convert 20 or 23 to bromocyclopropanes 21 and 22 by reaction with ethyl diazoacetate catalyzed by Rh2(OAc)4 were futile. By contrast, 2,3-dibromopropene (19) afforded smoothly (E)- and (Z)-dibromocyclopropane carboxylic esters 24 + 25. Alkylation of adenine (18) with 24 + 25 gave (E)- and (Z)-bromo derivatives 21 + 22. Base-catalyzed elimination of HBr resulted in the formation of (Z)- and (E)-methylenecyclopropanecarboxylic esters 26 + 27. More convenient one-pot alkylation-elimination of adenine (18) or 2-amino-6-chloropurine (30) with 24 + 25 afforded (Z)- and (E)-methylenecyclopropane derivatives 26 + 27 and 31 + 32. The Z-isomers were always predominant in these mixtures (Z/E approximately 2/1). Reduction of 26 + 27 and 31 + 32 with DIBALH afforded (Z)- and (E)-methylenecyclopropane alcohols 14 + 16 and 33 + 34. The latter were resolved directly by chromatography. Compounds 14 + 16 were converted to N6-(dimethylamino)methylene derivatives 28 and 29 which were separated and deprotected to give 14 and 16. Reaction of 33 and 34 with HCO2H led to guanine analogues 15 and 17. The 1H NMR spectra of the Z-analogues 14 and 15 are consistent with an anti-like conformation of the nucleobases. By contrast, 1H NMR and IR spectra of bromo ester 21 are indicative of syn-conformation of adenine. Several Z-(hydroxymethyl)methylenecyclopropanes exhibited in vitro antiviral activity in micromolar or submicromolar range against human and murine cytomegalovirus (HCMV and MCMV), Epstein-Barr virus (EBV), human herpes virus 6 (HHV-6), varicella zoster virus (VZV), and hepatitis B virus (HBV). Analogues 14, 15, and 33 were the most effective agents against HCMV (IC50 1-2.1, 0.04-2.1, and 0.8-5.6 microM), MCMV (IC50 2.1, 0.3, and 0.3 microM) and EBV in H-1 (IC50 0.2, 0.3, and 0.7 microM) and Daudi cells (IC50 3.2, 5.6, and 1.2 microM). Adenine analogue 14 was active against HBV (IC50 2 microM), VZV (IC50 2.5 microM), and HHV-6 (IC50 14 microM). Synadenol (14) and the E-isomer (16) were substrates of moderate efficiency for adenosine deaminase from calf intestine. The E-isomer 16 was more reactive than Z-isomer 14. The deamination of 14 effectively stopped at 50% conversion. Synadenol (14) was also deaminated by AMP deaminase from aspergillus sp.

Calculated RF electric field and temperature distributions in RF thermal ablation: comparison with gel experiments and liver imaging

The present paper is a study of theoretic modeling and experimental tests of that modeling for the local heating due to radiofrequency thermal ablation. A model is developed for the current and the associated electric field produced by a radiofrequency ablation probe. The temperature distributions resulting from the induced ohmic currents in the surrounding material are considered. A comparison is made between the theoretic temperature profiles and the shapes of thermal ablation 'lesions' produced in a controlled gelatin sample experiment. Comparison with the contours of human thermally induced liver lesions found in MRI studies also provides a validation of the success of the modeling. Successful modeling should lead to methods for optimization of the ablation procedure, especially as it is used in interventional MRI.

Structure-activity relationships of 2'-deoxy-2',2'-difluoro-L-erythro-pentofuranosyl nucleosides

Following the recent discoveries that some L-nucleosides are more or equal potent than their D-counterparts, we synthesized 2'-deoxy-2',2'-difluoro-L-erythro-pentofuranosyl nucleosides as potential antiviral agents. The target compounds were synthesized via the key intermediates 7a or 7b from L-gulono gamma-lactone. Compound 2 was oxidatively cleaved and coupled with ethyl bromodifluoroacetate in the presence of activated zinc under Reformatsky conditions to obtain a diasteomeric mixture of 4(R) and 4(S), in a 4:1 ratio. The major 4(R) isomer was cyclized and treated appropriately to obtain the mesylate 8a or 8b, which was condensed with various silyl-protected pyrimidines. Condensation of the alcohol 7a or 7b with 6-chloropurine under Mitsunobu conditions afforded the 6-chlorpurine analogs 53a or 53b and 54a or 54b. Further treatment of the compounds 53a, 54a and 53b, 54b afforded the inosine and adenine derivatives 57-60, respectively. The condensation of 2-amino-6-chloropurine with compound 8a and subsequent treatment with 2-mercaptoethanol/sodium methoxide afforded the guanine analogs 63 and 64. All of the synthesized nucleosides 31-52, 57-60, 63, and 64 were evaluated for antiviral activity and for cellular toxicity. Adenine derivative 57 showed a moderate activity against HIV-1 in PBM cells (3.4 microM). None of the other compounds showed any significant activities against HIV-1, HBV, HSV-1, HSV-2, and toxicity in Vero, CEM, and PBM cell lines up to 100 microM. The X-ray structure of the 5-iodocytosine analog showed a 2'-exo/3'-endo conformation for the carbohydrate moiety, which is different from those of the biologically active compounds (-)-FTC and L-FMAU.

Acute and Delayed Toxicity Studies on the Antiherpesvirus Agents 5-Methoxymethyl-2′-Deoxycytidine and 5-Methoxymethyl-2′-Deoxyuridine

5-Methoxymethyl-2′-deoxycytidine (MMdCyd) and the corresponding deoxyuridine analogue, 5-methoxymethyl-2′-deoxyuridine (MMdUrd) are selective antiherpesvirus agents. MMdCyd (ED501.5 μM) is a more potent inhibitor of herpes simplex virus replication than MMdUrd (ED5030 μM) when maintained in the deoxycytidine form (deamination prevented). The 5′-triphos-phates, MMdCTP and MMdUTP, were synthesized, and incorporation into DNA by mitochondrial DNA polymerase γ was investigated. MMdCTP and MMdUTP were incorporated into DNA in place of dCTP and dTTP, respectively. The effect of MMdCyd and MMdUrd on cell growth (acute toxicity) and prolonged exposure (delayed cytotoxicity) in CEM cells was investigated. The two analogues did not exhibit acute or delayed toxicity (2 weeks exposure) up to 1000 μM. In contrast, at a concentration as low as 0.125 μM of 2′,3′-dideoxycytidine (ddC; control drug), the doubling time of the cells increased after 10 days. At higher concentrations, a very marked increase in doubling time was observed from 6 days onward with ddC treatment. The data suggest that in uninfected cells neither MMdUrd nor MMdCyd are anabolized to the triphosphate form in significant amounts. As a result, little or no MMdCTP or MMdUTP builds up in the mitochondria and thus delayed toxicity is not observed.

Synthesis and anti-hepatitis B virus activity of 9-(2-deoxy-2-fluoro-beta-L-arabinofuranosyl) purine nucleosides

Since the discovery of 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU) as a potent anti-HBV and anti-EBV agent, we have studied the structure-activity relationships of 2'-deoxy-2'-fluoro-beta-L-arabinofuranosylpyrimidine nucleosides as anti-HBV agents. Therefore it is rational to extend this study to the purine nucleosides. Thus, 3,5-di-O-benzoyl-2-deoxy-2-fluoro-beta-L-arabinofuranosyl bromide (1), which was prepared from L-xylose via a multistep procedure, was coupled with several purines by the sodium salt method. From this general synthesis, 10 purine nucleosides containing the 2-deoxy-2-fluoro-beta-L-arabinofuranosyl moiety have been obtained. The anti-HBV activity and toxicity of the synthesized nucleosides were evaluated in HepG2 2.2.15 cells. Among them, the adenine (10) and hypoxanthine (15) derivatives exhibit good in vitro anti-HBV activity (EC50 = 1.5 and 8 microM, respectively) without significant toxicity up to 200 microM.

Antitumor agents--CLXXIII. Synthesis and evaluation of camptothecin-4 beta-amino-4'-O-demethyl epipodophyllotoxin conjugates as inhibitors of mammalian DNA topoisomerases and as cytotoxic agents

Two conjugates composed of a camptothecin and a 4'-O-demethyl epipodophyllotoxin derivative joined by an imine linkage were prepared and evaluated as inhibitors of mammalian DNA topoisomerases I and II. Target compounds stimulated cleavable complex formation with both types of enzyme in vitro although activities were reduced at least twofold relative to the activity of unconjugated constituents. The behavior of the most active conjugate as an inhibitor of cell growth closely resembled both topoisomerase I- and II- inhibitory components in that the compound displayed a combined spectrum of activity against various drug-resistant KB sublines. Cytotoxic activity and selectivity were largely retained through conjugation, the exception being a lower than expected activity against a pleiotrophic multidrug-resistant subline. The induced levels and the properties of cellular protein-associated DNA complexes were consistent with topoisomerase involvement and with the in vitro cleavage assay results. Based on the present findings, conjugation afforded cleavable complex-forming topoisomerase inhibitors which display dual target specificity and a broad spectrum of cytotoxic activity against drug-resistant cells.

Inhibition of replication of hepatitis B virus by cytallene in vitro

The acyclic cytosine nucleoside analog cytallene [1-(4'-hydroxy-1',2'-butadienyl)cytosine], which has both (+)- and (-)-enantiomers, was evaluated for its anti-hepatitis B virus (HBV) activity in 2.2.15 cells and was found to have potent activity against HBV DNA synthesis. The R-(-)-enantiomer was found to be the more active of the cytallene enantiomers, with a 50% inhibition concentration against HBV synthesis (HBIC50) of 0.08 microM. Its antiviral activity could be reversed by deoxycytidine (dC) and less efficiently by cytidine. Upon removal of the R-(-)-enantiomer from culture medium, the synthesis of HBV DNA could reinitiate, which suggested that the antiviral action is reversible. The R-(-)-enantiomer was also found to be more cytotoxic than the S-(+)-enantiomer. The degree of cytotoxicity varied among the cell lines, with a 50% inhibition of cell growth at greater than 10 microM. The R-(-)-enantiomer had no effect on HBV RNA synthesis and mitochondrial DNA synthesis at a concentration of 10 times or more than the HBIC50. The two enantiomers cannot be deaminated by dC deaminase, and they can be phosphorylated by cytoplasmic dC kinase. The R-(-)-enantiomer of cytallene is the first acyclic cytosine analog with potent inhibitory activity against HBV similar to those of other L-(-)-ddC analogs.

Altered formation of topotecan-stabilized topoisomerase I-DNA adducts in human leukemia cells

Topotecan (TPT) is a topoisomerase I (topo I) poison that has shown promising antineoplastic activity in solid tumors and acute leukemia. In the present study, a band depletion assay was used to evaluate the ability of TPT to stabilize topo I-DNA adducts in human leukemia cell lines and in clinical leukemia samples ex vivo. This assay showed that 50% of the cellular topo I in HL-60 human myelomonocytic leukemia cells became covalently bound to DNA at an extracellular TPT concentration of 4 micromol/L. In contrast, in 13 clinical specimens of human leukemia harvested before treatment of patients with TPT, the TPT concentration required to stabilize 50% of the cellular topo I in topo I-DNA complexes ranged from 3 to greater than 100 micromol/L (median, 30 micromol/ L). Flow microfluorimetry showed that cellular TPT accumulation varied over only a twofold range and failed to provide evidence for transport-mediated resistance in the clinical samples. These observations raise the possibility that formation of topo I-DNA adducts is diminished in many specimens of refractory/relapsed acute leukemia by a mechanism that might alter topo I sensitivity to TPT.

Dose-escalation and pharmacodynamic study of topotecan in combination with cyclophosphamide in patients with refractory cancer

PURPOSE

Based on preclinical data that demonstrated synergy between alkylating agents and topoisomerase (topo) I poisons, we determined the maximum-tolerated dose (MTD) of topotecan, using a 5 day bolus schedule, that could be given in combination with a single, fixed dose of cyclophosphamide. Pharmacodynamics of this combination were explored by analyzing biochemical effects of treatment in peripheral-blood mononuclear cells (PBMCs).

PATIENTS AND METHODS

Patients with refractory cancer were treated with cyclophosphamide 600 mg/m2 on day 1, followed by topotecan given as a 30-minute infusion for 5 consecutive days. Cycles were repeated every 3 weeks. Once the MTD was defined, granulocyte colony-stimulating factor (G-CSF) was added to the regimen in an attempt to escalate further the dose of topotecan. Plasma concentrations of topotecan were determined during the first treatment cycle by high-performance liquid chromatography. PBMCs were sampled at baseline and throughout the 5-day treatment period for analysis of topo I protein concentrations and to determine drug-induced DNA fragmentation.

RESULTS

Twenty-six patients were treated with topotecan at doses that ranged from 0.5 mg/m2/d to 1.2 mg/ m2/d for a total of 74 cycles. Reversible neutropenia was dose-limiting, with mild to moderate suppression of the other blood-cell elements commonly occurring. Transfusions of RBCs and platelets were required in 24% and 7% of treatment cycles, respectively. The most prominent nonhematologic toxicities were fatigue and weight loss. Compared with previously published data in which topotecan was administered alone, cyclophosphamide did not appear to alter the pharmacokinetics of topotecan. Significant increases in topo I concentration were identified in PBMCs following the administration of cyclophosphamide on day 1 and there was a significant decrease in topo 1 during the 5-day course of treatment (P < .01, sign test). DNA fragmentation as a result of drug treatment was identified in 11 of 15 (73%) cycles analyzed.

CONCLUSION

For previously treated patients, the recommended dose of topotecan in this schedule is 0.75 mg/m2/d without growth factor support and 1.0 mg/ m2/d if it is administered with G-CSF. Biochemical changes in cells induced by exposure to camptothecins can be measured in vivo and these effects may have important implication in the design of combination therapies and the optimal scheduling of this class of agents.