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W R Wilson

Publications and source records attributed to W R Wilson.

At least 109 records · Page 6Linked to original sources
PubMed1995

Hypoxia-selective antitumor agents. 11. Chlorambucil N-oxide: a reappraisal of its synthesis, stability, and selective toxicity for hypoxic cells.

The potential hypoxia-selective cytotoxin 4-[4'-[N,N-bis(2"-chloroethyl)amino]phenyl]butanoic acid N-oxide (chlorambucil N-oxide, 4) was synthesized and characterized as its hydrochloride salt. This compound was shown to be unstable, decomposing in some organic solvents to the hydroxylamine 4-[4'-[N-(2"-chloroethoxy)-N-(2"-chloroethyl)amino]phenyl]butanoic acid (11) by a mechanism previously demonstrated for aliphatic mustard N-oxides and under aqueous conditions to a more complex mixture, of which the predominant components were the monochloroethyl derivative 7 and formaldehyde. Comparison of NMR spectra showed that a recent published synthesis of 4 in fact resulted in the rearrangement product 11, indicating that recent reported investigations of the hypoxia-selective cytotoxicity and metabolism of chlorambucil N-oxide have examined this rearrangement product rather than 4. In a clonogenic assay, 4 was less cytotoxic against AA8 cells than was chlorambucil, but the effect of oxygen on cytotoxicity was no greater than for chlorambucil itself.

Cell Survival↗
PubMed1995

N-[2-(2-methyl-5-nitroimidazolyl)ethyl]-4-(2-nitroimidazolyl)butanamide (NSC 639862), a bisnitroimidazole with enhanced selectivity as a bioreductive drug.

Compounds containing two redox centers, both of which must be reduced for full expression of cytotoxicity by oxygen-inhibitable pathways (bis-bioreductive drugs), have potential as cytotoxins with high selectivity for hypoxic tumor cells. The bisnitroimidazole N-[2-(2-methyl-5-nitroimidazolyl)ethyl]-4-(2-nitroimidazolyl)butanamide (NNB, NSC 639862), in which a 2-nitroimidazole and 5-nitroimidazole moiety are joined via a carboxamide linker, is highly selective for hypoxic AA8 Chinese hamster cells (200-fold by 8 h) relative to mononitroimidazoles (5-25-fold). A bis-bioreductive mechanism is consistent with the marked increase in hypoxic potency and selectivity of NNB with time and the apparent requirement that the two nitro groups be present in the same molecule. NNB differed from mononitroimidazoles in inducing fewer DNA single strand breaks at equivalent toxicity, suggesting that a duplex DNA lesion (locally doubly damaged site) may be responsible for cell killing. Alkaline elution studies and the lack of hypersensitivity of the repair-defective UV4 cell line indicate that the cytotoxic lesion is not a DNA interstrand cross-link. NNB shows greater hypoxic selectivity than the alkylating 2-nitroimidazole RB 6145 against AA8 cells and is active in combination with radiation when administered in multiple doses against the MDAH-MCa-4 mouse mammary carcinoma.

Aerobiosis↗
PubMed1995

Hypoxia-activated prodrugs as antitumour agents: strategies for maximizing tumour cell killing.

1. Hypoxia arises in solid tumour because of inefficient blood supply. While hypoxic cells are resistant to radiotherapy and probably to many chemotherapeutic drugs they can, in principle, be turned to advantage through the development of hypoxia-activated cytotoxic drugs (bioreductive drugs). 2. Three general approaches to exploiting tumour hypoxia are discussed. The first relies on fluctuating blood flow in tumours and the consequent cycling of cells through the hypoxic compartment. The second incorporates a prodrug approach in which drug activation gives rise to cytotoxic metabolites which diffuse out of hypoxic zones. The third utilizes selective inhibitors of tumour blood flow to induce additional hypoxia and thus enhance bioreductive drug activation. 3. The latter two approaches are illustrated by recent studies with the dinitrobenzamide nitrogen mustard class of bioreductive drugs and their combination with the tumour blood flow inhibitor 5,6-dimethylxanthenone-4-acetic acid.

Aniline Mustard↗
PubMed1995

Effective treatment of cephalosporin-rifampin combinations against cryptic methicillin-resistant beta-lactamase-producing coagulase-negative staphylococcal experimental endocarditis.

The efficacy of cefazolin or cefpirome alone or combined with rifampin was compared with that of vancomycin alone or combined with rifampin in an experimental model of methicillin-resistant, beta-lactamase-producing, coagulase-negative staphylococcal endocarditis. Phenotypically, the mecA gene-positive strain used in vivo did not exhibit methicillin resistance by the agar dilution or disk susceptibility method but was resistant in vitro (oxacillin MIC, 64 micrograms/ml) by the microtiter dilution method with 2% NaCl supplementation. Macrodilution broth susceptibilities of standard inocula failed to demonstrate cross-resistance of staphylococci to cefazolin (MIC, 8 micrograms/ml) or cefpirome (MIC, 4 micrograms/ml). In vivo, vancomycin and cefpirome had similar activities, and both regimens were more effective than was cefazolin alone. While the MIC of rifampin was low (0.031 micrograms/ml), monotherapy with rifampin resulted in a bimodal distribution of outcomes due to the expected emergence of resistant mutants. The results in vitro of time-kill synergy studies using rifampin in combination with cefazolin or cefpirome varied with the antimicrobial concentrations tested and did not reliably predict activities in vivo of rifampin-beta-lactam combination therapies. Cefpirome, but not cefazolin or vancomycin, in combination with rifampin was synergistic in vivo. Cefpirome in combination with rifampin was more effective than was cefazolin in combination with rifampin. Both cephalosporin-rifampin regimens were significantly more effective than was cephalosporin or vancomycin monotherapy and were as effective as vancomycin combined with rifampin. These data support further evaluation of rifampin-beta-lactam combinations as possible alternative therapies to vancomycin-containing regimens for selected methicillin-resistant coagulase-negative staphylococcal infections.

Animals↗
PubMed1995

Experience with percutaneous endoscopic gastrostomy on an otolaryngology service.

Seventy-one patients have undergone percutaneous endoscopic gastrostomy (PEG) on our otolaryngology service. Most commonly, these were neurologically-impaired (63%) or head and neck cancer (31%) patients. The PEG procedures were done, in almost all instances, in the operating room in conjunction with other indicated ORL-HNS procedures such as tracheotomy (71%) or with endoscopy or resection for head and neck cancer. The success rate in placement of the gastrostomy was 98%. There was one major complication, namely, seeding of the gastrostomy site with squamous cell carcinoma from a hypopharyngeal tumor. We conclude that PEG is a useful addition to the armamentarium of the head and neck surgeon.

Adult↗
PubMed1994

DNA-directed alkylating agents. 6. Synthesis and antitumor activity of DNA minor groove-targeted aniline mustard analogues of pibenzimol (Hoechst 33258)

A series of nitrogen mustard analogues of the DNA minor groove binding fluorophore pibenzimol (Hoechst 33258) have been synthesized and evaluated for antitumor activity. Conventional construction of the bisbenzimidazole ring system from the piperazinyl terminus, via two consecutive Pinner-type reactions, gave low yields of products contaminated with the 2-methyl analogue which proved difficult to separate. An alternative synthesis was developed, involving construction of the bisbenzimidazole from the mustard terminus, via Cu(2+)-promoted oxidative coupling of the mustard aldehydes with 3,4-diaminobenzonitrile to form the monobenzimidazoles, followed by a Pinner-type reaction and condensation with 4-(1-methyl-4-piperazinyl)-o-phenylenediamine. This process gives higher yields and pure products. The mustard analogues showed high hypersensitivity factors (IC50AA8/IC50 UV4), typical of DNA alkylating agents. There was a large increase in cytotoxicity (85-fold) across the homologous series which cannot be explained entirely by changes in mustard reactivity and may be related to altering orientation of the mustard with respect to the DNA resulting in different patterns of alkylation. Pibenzimol itself (which has been evaluated clinically as an anticancer drug) was inactive against P388 in vivo using a single-dose protocol, but the short-chain mustard homologues were highly effective, eliciting a proportion of long-term survivors.

Alkylating Agents↗
PubMed1994

Metabolic and radiolytic reduction of 4-alkylamino-5-nitroquinoline bioreductive drugs. Relationship to hypoxia-selective cytotoxicity.

The 4-alkylamino-5-nitroquinolines (5NQs) are a new series of bioreductive drugs that exhibit varying degrees of selective toxicity (up to 60-fold) under hypoxic conditions in cell culture. This study tested the hypothesis that differences in hypoxia-selective cytotoxicity in this series reflect differences in the efficiency with which oxygen inhibits metabolic reduction. The products of reduction of six 5NQs were characterized and rates of reduction compared in aerobic and hypoxic AA8 cells. The major stable products of both radiolytic and metabolic reduction under anoxic conditions were the corresponding amines, which were not responsible for the toxicity of the parent nitro compounds. Metabolism of each compound was inhibited completely in aerobic cells, indicating that differences in hypoxia-selective toxicity in this series are not due to variations in efficiency as substrates for oxygen-insensitive nitro reduction. Rates of hypoxic metabolism correlated broadly with hypoxia-selective cytotoxicity; the 5NQ derivatives with high rates of hypoxic metabolism had good hypoxia-selective cytotoxicity, whereas the compounds with low rates of reduction (the 3,6-dimethyl and 8-methylamino compounds; 3,6diMe-5NQ and 8NHMe-5NQ) were non-selective. Low rates of drug-induced oxygen consumption by 3,6-diMe-5NQ and 8NHMe-5NQ in respiration-inhibited cells confirmed that these compounds are poor substrates for enzymatic nitro reduction. While there was an overall correlation between one-electron reduction potential at pH 7 (E1(7)) and rate of metabolic reduction, the relatively high E1(7) of 3,6diMe-5NQ (-367 mV) indicates that rates of reduction, and hypoxic selectivity of cytotoxicity, cannot be predicted from reduction potential alone. 3,6diMe-5NQ and 8NHMe-5NQ are cytotoxic through a non-bioreductive mechanism, the variable contribution of which may underlie the differences in hypoxia-selective cytotoxicity within this series of bioreductive drugs.

Aminoquinolines↗
PubMed1994

Hypoxia-selective antitumor agents. 9. Structure-activity relationships for hypoxia-selective cytotoxicity among analogues of 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide.

A series of analogues of the novel hypoxia-selective cytotoxin 5-[N,N-bis(2-chloroethyl)amino]-2,4-dinitrobenzamide (6) have been prepared and evaluated, in a search for compounds which retain high hypoxic selectivity but have increased potency and/or aqueous solubility. Several analogues with ionizable or dipolar carboxamide side chains showed improved solubility but generally had reduced cytotoxic potency and hypoxic selectivity. Modification of the mustard leaving groups or replacement of the carboxamide moiety provided some compounds with superior potency, but only the mixed chloro/mesylate mustard 20 provided a gain in potency relative to solubility while retaining the hypoxic selectivity of 6. These nitrogen mustards did not show the remarkable activity demonstrated by the related aziridine 7 [CB 1954, 5-(N-aziridinyl)- 2,4-dinitrobenzamide] in Walker 256 adenocarcinoma cells and are not efficient substrates for the DT-diaphorase which activates the latter compound by aerobic nitroreduction in Walker cells. Variations in hypoxic selectivity within the dinitrobenzamide mustards appear not to be due to differences in sensitivity to activation by this enzyme. Walker cells showed intermediate sensitivity to the mono(2-chloroethyl) analogue 26 but not to the related half-mustard 27, suggesting that the inhibition of DT-diaphorase activity is due to steric effects in the 5-position. The preferred compound overall with respect to solubility, potency, and in vitro hypoxic cell selectivity was the (dimethylamino)-ethyl derivative 11. DNA elution studies and comparison of the sensitivity of AA8 and UV4 cells to this compound indicated reductive activation to form a DNA cross-linking agent under hypoxia. Radiobiological studies indicated 11 to be equally active against both aerobic and hypoxic cells in KHT tumors. It is not clear whether this reflects efficient killing of aerobic cells as a result of diffusion of reduced metabolites from hypoxic regions or whether cytotoxicity in tumors is independent of hypoxia.

Aniline Mustard↗
PubMed1994

Does DNA targeting affect the cytotoxicity and cell uptake of basic nitroquinoline bioreductive drugs?

PURPOSE: A series of 4-(N,N-dimethylaminopropylamino)-5-nitroquinoline bioreductive drugs was studied to determine whether DNA binding influences cytotoxic potency, hypoxic selectivity or cellular uptake in cell culture. METHODS AND MATERIALS: Cytotoxicity was assessed by clonogenic assay of stirred suspension cultures of aerobic (20% O2) or hypoxic (< 10 ppm O2) late log-phase AA8 cells. Drug uptake was measured by high performance liquid chromatography of acetonitrile-extracted cell pellets and extracellular medium, or by using radiolabelled drug. Drug binding to calf-thymus DNA was measured by equilibrium dialysis. Intracellular pH was determined using the [14C]-5,5-dimethyl-2,4-oxazolidinedione method and intralysosomal pH using the fluorescein isothiocyanate-labelled dextran method. RESULT: The compounds were weak DNA binders under physiological conditions, with association constants in the range 25-480 M-1. There was no correlation between DNA binding affinity and hypoxic or aerobic cytotoxic potency, or hypoxic selectivity. These compounds were accumulated by cells to high concentrations (25-60 fold higher than extracellular), but cell uptake also showed no relationship to DNA binding affinity. Ammonium chloride selectively raised intralysosomal pH and inhibited the cellular accumulation of these drugs. CONCLUSION: These results indicate that DNA binding is not the major determinant of cytotoxic potency, hypoxic selectivity, or cellular uptake of the 5-nitroquinolines. Instead, the variable contribution of a nonbioreductive mechanism of toxicity appears to underlie the differences in cytotoxic potency and hypoxic selectivity within this series. The high intracellular drug concentrations of these diprotic bases appear to be due primarily to lysosomal uptake rather than DNA binding. Lysosomal uptake might restrict diffusion of basic bioreductive drugs to the target hypoxic regions of solid tumors.

Animals↗
PubMed1994

Nitrobenzyl mustard quaternary salts: a new class of hypoxia-selective cytotoxins capable of releasing diffusible cytotoxins on bioreduction.

PURPOSE: To explore the utility of a new class of compounds, nitrobenzyl mustard quaternary salts, as hypoxia-selective prodrugs of diffusible cytotoxins. METHODS AND MATERIALS: The parent compound N,N-bis(2-chloroethyl)-N-methyl-N-(2-nitrobenzyl)ammonium chloride (SN 25246) was prepared by reaction of 2-nitrobenzyl chloride with N-methyldiethanolamine, and reaction of the resulting quaternary diol with thionyl chloride at room temperature. The rate of release of mechlorethamine from this compound in the presence of cells under aerobic and hypoxic conditions was determined by trapping with diethyldithiocarbamate. Cytotoxicity was assessed by clonogenic assay of stirred suspension cultures of EMT6 cells, and also in intact and dissociated EMT6 spheroids. In vivo activity was evaluated in mice bearing SC KHT tumors. RESULTS: The parent compound is a stable, water-soluble compound with an E(1) of -369 mV. It releases mechlorethamine, and shows selective toxicity towards hypoxic EMT6 cells in culture, increasing with time to several 1000-fold after 4 h. It is much more active against intact than dissociated EMT6 spheroids, and shows low but statistically significant activity against KHT tumors in vivo. CONCLUSION: Nitrobenzyl mustard quaternary salts are a new class of hypoxia-selective cytotoxin. The parent compound shows very high selectivity for hypoxic cells in vitro, and undergoes reduction in hypoxic cells, releasing mechlorethamine which can back-diffuse to kill surrounding oxygenated cells.

Animals↗
PubMed1994

Exploiting tumor hypoxia through bioreductive release of diffusible cytotoxins: the cobalt(III)-nitrogen mustard complex SN 24771.

PURPOSE: To assess the oxygen dependence of a novel cobalt-nitrogen mustard complex, SN 24771, designed to release a diffusible cytotoxic metabolite in hypoxic tumor microenvironments. METHODS AND MATERIALS: Oxygen dependence of cell killing was assessing in well-stirred single cell suspensions obtained by enzymatic dissociation of EMT6 spheroids, using a sensitive oxygen electrode to measure oxygen concentrations in solution. Cell killing in intact EMT6 spheroids was also compared with that in single cell suspensions. RESULTS: Cytotoxicity of SN 24771 in single cell suspensions was inhibited by very low concentrations of oxygen. The C50 value (O2 required for 50% inhibition of log cell kill) was ca. 0.02% O2 at 1 h, and the K value (O2 required to give a cytotoxic potency equal to the average of that at zero and infinite O2) was of a similar order. However, intact spheroids were much more sensitive to SN 24771 than could be accounted for by the K curve for single cell suspensions, this estimate being based on published data for the oxygen concentration profile in these spheroids. CONCLUSION: The cytotoxicity of SN 24771 is inhibited appreciably at oxygen concentrations which are too low to provide radiosensitization. In this respect, SN 24771 resembles organic bioreductive drugs such as quinones and nitroaromatic compounds. However, the extensive killing observed in multicellular spheroids is consistent with release of a diffusible nitrogen mustard on reduction. Bioreductive drugs with a low K value for activation, but which release a diffusible cytotoxin, may have desirable properties as tumor radiosensitizers.

Antineoplastic Agents↗
PubMed1994

Combining bioreductive drugs (SR 4233 or SN 23862) with the vasoactive agents flavone acetic acid or 5,6-dimethylxanthenone acetic acid.

PURPOSE: To determine whether 5,6-dimethylxanthenone acetic acid (DMXAA), a potent analogue of flavone acetic acid (FAA) inhibits blood flow in mouse mammary tumors, and to assess whether DMXAA enhances the antitumor effects of Tirapazamine (SR 4233) and the novel bioreductive drug SN 23862 (a dinitrobenbenzene mustard). METHODS AND MATERIALS: MDAH-MCa-4 mouse mammary tumors were grown i.m. in the leg of C3H/HeN mice. Tumor blood flow was assessed by the pertechnetate clearance method and subsequent growth delay was determined in the same tumors. RESULTS: Administration of DMXAA (65-70 mumol/kg) resulted in inhibition of tumor blood flow to approximately 25% of control values, with no recovery observed up to 36 h post-treatment. Combination of DMXAA with SR 4233 provided a significant increase in tumor growth inhibition relative to either drug alone. In this effect, DMXAA was qualitatively similar to FAA, but was approximately 10 x more potent. The interaction between DMXAA (65 mumol/kg) and SR 4233 (200 mumol/kg) was maximal with SR 4233 given between 15 min before and 60 min after DMXAA. For SN 23862, a similar enhanced growth delay was observed in combination with DMXAA, with no obvious time dependence between 15 min before and 4 h after DMXAA. When mean values for groups treated with SR 4233 (200 mumole/kg) alone and in combination with DMXAA (65-90 mumole/kg) were compared, a correlation was observed between tumor blood flow inhibition and subsequent growth delay. CONCLUSION: DMXAA is a potent inhibitor of blood flow in MDAH-MCa-4 tumors. Combination of this vasoactive drug with bioreductive agents leads to an enhanced antitumor effect. For SR 4233 and DMXAA, this enhanced effect may be predictable by measurement of tumor blood flow inhibition shortly after drug administration.

Aniline Mustard↗
PubMed1994

Hypoxia-selective antitumor agents. 8. Bis(nitroimidazolyl)alkanecarboxamides: a new class of hypoxia-selective cytotoxins and hypoxic cell radiosensitisers.

A series of novel bis(nitroimidazolyl)alkanecarboxamides has been prepared and evaluated for hypoxia-selective cytotoxicity and hypoxic cell radiosensitisation in vitro and in vivo. The compounds were prepared by direct coupling of preformed side chain acid and amine components, using diethyl phosphorocyanidate at room temperature. Although designed to be bis-bioreductive prodrugs of DNA cross-linking agents, none of the compounds showed evidence of DNA cross-linking activity, being equally potent against cell lines deficient and proficient in repair of cross-links. However, one of these compounds, N-[2-(2-methyl-5-nitro-1H-imidazolyl)ethyl]-4-(2-nitro-1H- imidazolyl)butanamide (10; SN 24699), showed high hypoxic selectivity as a cytotoxin (rising to 200-fold after exposure to the drug for several hours) in the repair-proficient Chinese hamster cell line AA8. This selectivity was greater than observed for the alkylating 2-nitroimidazole (4; RB 6145) (40-fold) or simple mononitroimidazoles (5-25-fold). Investigation of structure-activity relationships for hypoxic selectivity of bis(nitroimidazoles) was restricted by their low aqueous solubility, but a certain minimum separation of the two nitroimidazole units (by more than five atoms) appears desirable. All the compounds radiosensitized hypoxic cells in vitro but were little more potent as radiosensitizers than the corresponding monomeric nitroimidazoles. Compound 10 caused additional cell killing in the KHT tumor when multiple drug doses were administered in combination with a single dose of radiation. It is not yet clear whether this activity reflects hypoxic cell radiosensitization or cytotoxicity toward hypoxic cells, but this new class of bis-bioreductive agent clearly warrants further investigation.

Aerobiosis↗
PubMed1994

The Onchocerca volvulus homologue of the multifunctional polypeptide protein disulfide isomerase.

Protein disulfide isomerase (PDI) functions to catalyze the formation of correct disulfide bonds in nascent proteins, and also acts as one of the subunits of prolyl-4 hydroxylase, the enzyme responsible for the oxidative maturation of procollagen. Since the cuticle of parasitic nematodes consists primarily of a network of collagen molecules which are connected through intermolecular disulfide bonds, PDI might be expected to be involved in the process of cuticle biosynthesis. The isolation and characterization of a cDNA encoding the PDI homologue of Onchocerca volvulus is described. This cDNA contains a single, long open reading frame that encodes sequence motifs identical to the two known active sites of PDI for isomerase activity. The O. volvulus PDI appears to be encoded by a single copy gene. Both in situ hybridization and immunolocalization data suggest that PDI is both spatially and temporally regulated in O. volvulus. The pattern of spatial and temporal regulation is consistent with the involvement of PDI in the biosynthesis of the parasite cuticle. The parasite protein appears to be an antigen recognized by a minority of individuals exposed to O. volvulus.

Amino Acid Sequence↗
PubMed1994

Oxygen dependence of the cytotoxicity and metabolic activation of 4-alkylamino-5-nitroquinoline bioreductive drugs.

The cytotoxic potency of 4-alkylamino-5-nitroquinoline drugs in AA8 cell cultures is enhanced up to 60-fold under hypoxia, with wide variations in selectivity for hypoxic cells observed for different members of this series. This study uses three representative 5-nitroquinolines to examine whether these differences in hypoxia-selective cytotoxicity are cell line specific, and to explore quantitatively the oxygen dependence of the cytotoxicity and metabolism of these compounds. The parent compound 5NQ, its 5NQ, its 8-methyl analogue (8Me5NQ) and the 8-methylamino analogue (8NHMe-5NQ) each showed similar hypoxic selectivity (ratio of concentration x time for 90% kill for zero versus 20% oxygen of 13-18-, 30-69- and 1.2-1.4-fold respectively in the three cell lines tested (AA8 Chinese hamster ovary, EMT6/Ak mouse mammary tumour and FME human melanoma). The cytotoxicity and metabolism (covalent binding) of radiolabelled 8Me-5NQ was investigated in AA8 cultures over a range of oxygen tensions (0-95%). The oxygen tension in solution required for 50% inhibition of log cell kill or adduct formation observed under anoxia (C50) was 0.01 and 0.02% oxygen respectively, suggesting that bioreductive alkylation is the mechanism of 8Me-5NQ toxicity. The K-value (oxygen concentration for cytotoxic potency equal to the mean of the potencies at zero and infinite oxygen) was similar (0.02% oxygen). Calculations based on measured rate constants for formation of the nitroradical anion of 8Me-5NQ and rates of radical loss through disproportionation or reaction with oxygen, predict a K-value for 8Me-5NQ of 0.025% oxygen, in good agreement with the experimentally determined value. Modelling of cell killing expected by the combination of 8Me-5NQ plus radiation suggested that tumour cells at intermediate oxygen tensions (0.01-1%) will be partially resistant to this treatment, and would limit the use of these 5-nitroquinolines in combination with radiation, unless sufficient drug could be delivered to cause extensive killing in the anoxic compartment.

Animals↗