Preparation and surface characterization of HMDI-activated 316L stainless steel for coronary artery stents.

Poor compatibility between blood and metallic coronary artery stents is one reason for arterial restenosis. Immobilization of anticoagulant agents on the stent's surface is feasible for improving compatibility. We examined possible surface-coupling agents for anticoagulant agent immobilization. Hexamethylene diisocyanate (HMDI) and 3-aminopropyl-triethoxysilane (APTS) were examined as surface-coupling agents to activate 316L stainless steel (e.g., stent material). The activated surface was characterized using Fourier transformation infrared spectroscopy (FTIR), atomic force microscope (AFM), surface plasmon resonance (SPR), and trinitrobenzene sulfonic acid (TNBS) assay. In FTIR analysis, HMDI and APTS were both covalently linked to 316L stainless steel. In AFM analysis, it was found that the HMDI-activated surface was smoother than the APTS-activated one. In SPR test, the shift of SPR angle for the APTS-activated surface was much higher than that for the HMDI-activated surface after being challenged with acidic solution. TNBS assay was used to determine the amount of immobilized primary amine groups. The HMDI-activated surface was found to consist of about 1.32 micromol/cm(2) amine group, whereas the APTS-activated surface consisted of only 0.89 micromol/cm(2) amine group. We conclude that the HMDI-activated surface has more desirable surface characteristics than the APTS-activated surface has, such as chemical stability and the amount of active amine groups.

Evaluation of benzyl selenocyanate glutathione conjugate for potential chemopreventive properties in colon carcinogenesis.

Observational, clinical and experimental studies have suggested that dietary supplementation with selenium can inhibit the development of colon cancer. Since toxicity and chemopreventive efficacy of selenium compounds depend to a large extent, on the form of selenium the development of efficacious organoselenium compounds with low toxicity is being pursued in our laboratory. We have assessed the chemopreventive properties of a newly synthesized organoselenium compound, benzyl selenocyanate glutathione conjugate (BSeSG), and of benzyl selenocyanate (BSC), as a positive control, using azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) as a measure of efficacy. Five-week-old male F344 rats were fed the control diet (modified AIN-76A) or experimental diets containing 10 or 20 ppm BSeSG (1.7 and 3.4 ppm as Se, respectively), or 10 ppm BSC (4.1 ppm as Se). One week later, all animals except those in vehicle (normal saline)-treated groups were s.c. injected with AOM (15 mg/kg of body weight, once weekly for 2 weeks). All animals were sacrificed 7 weeks after the last AOM injection, and the ACF, levels of prostaglandin E2 (PGE2), cyclooxygenase protein expression (COX-1 and -2), and glutathione S-transferase type mu (GST-mu) were determined in the colon. As expected, dietary administration of BSC suppressed ACF development by about 37%. In rats administered 10 or 20 ppm BSeSG, the frequencies of AOM-induced colonic ACF were significantly decreased compared to those of rats given AOM and control diet by about 41% (P<0.01) and 61% (P<0.001), respectively. Administration of BSeSG inhibited PGE2 production (81-88% inhibition) via COX-2 synthesis in the colonic mucosa (18-60% inhibition). Also, BSeSG increased GST-mu protein activity in colonic mucosa (30-32% increase). These data suggest that a newly synthesized organoselenium compound, BSeSG might be a promising chemopreventive agent against colon carcinogenesis.

Chemoprevention of colon cancer by organoselenium compounds and impact of high- or low-fat diets.

BACKGROUND: Observational and experimental studies have suggested that dietary supplementation with selenium can inhibit the development of colon cancer. However, many forms of selenium are toxic. Consequently, the development of efficacious compounds with low toxicity has been pursued. PURPOSE: Two synthetic organoselenium compounds, p-methoxy-benzyl selenocyanate (p-methoxy-BSC) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC), were tested for their ability to inhibit colon carcinogenesis in rats that were treated with the carcinogen azoxymethane and fed low- or high-fat diets. METHODS: Groups of 5-week-old male F344 rats (42 animals/ group) were fed either a high-fat diet or a low-fat diet with or without added p-methoxy-BSC (10 or 20 parts per million [ppm]) or p-XSC (20 ppm). Two weeks later, 30 animals in each group received a subcutaneous injection of azoxymethane (15 mg/kg body weight); 1 week later, they received a second injection. The remaining 12 rats in each group received two injections of saline. Three days after the second injection of carcinogen or saline, animals being fed diets with p-methoxy-BSC or p-XSC were switched to corresponding organoselenium-free low- or high-fat diets for the remainder of the study to determine the effects of the selenium compounds on the initiation phase of colon carcinogenesis. At that time, groups of animals that had been maintained on organoselenium-free low- or high-fat diets were switched to diets containing p-methoxy-BSC or p-XSC until the end of the study to determine the effects of these compounds on the postinitiation phase of colon carcinogenesis. All animals were killed during the 38th week after azoxymethane or saline treatment, and histopathologic analysis of the colon tumors was performed. Colon tumor incidence and multiplicity were analyzed statistically. RESULTS: No obvious toxic effects were observed following dietary administration of 10 or 20 ppmp-methoxy-BSC or 20 ppm p-XSC. Administration of 20 ppm p-methoxy-BSC in a high-fat diet during the initiation and postinitiation phases of colon carcinogenesis significantly (statistically) reduced colon tumor incidence; 10 ppmp-methoxy-BSC in a high-fat diet significantly reduced colon tumor incidence but only when it was given during the postinitiation phase. Colon tumor incidence was also significantly reduced when 20 ppm p-XSC was given in a high-fat diet during the initiation phase of colon carcinogenesis. When 20 ppm p-XSC was administered in either a high-fat diet or a low-fat diet during the postinitiation phase, both colon tumor incidence and multiplicity were significantly reduced; the greatest reductions were in animals fed a low-fat diet. CONCLUSIONS: In this model system, p-methoxy-BSC and p-XSC are effective agents for the chemoprevention of colon cancer. The effects of p-XSC were enhanced in animals fed a low-fat diet.

Evaluation of organoselenium compounds for potential chemopreventive properties in colon cancer.

Our previous studies have demonstrated that dietary benzylselenocyanate (BSC) and 1,4-phenylenebis (methylene) selenocyanate (p-XSC); organoselenium compounds, act as potential chemopreventive agents in colon carcinogenesis in F344 rats. As a part of a program aimed to develop less toxic and more effective chemopreventive organoselenium compounds than inorganic selenium and BSC, we evaluated the positional isomers of BSC namely o-, m-, and p-methoxy BSC and dibenzyl diselenide (DDS) for their potential chemopreventive properties using colonic epithelial cell proliferation as an efficacy endpoint. p-XSC and inorganic selenium, which were found to inhibit colon carcinogenesis in earlier preclinical efficacy study, were included as positive controls. Male F344 rats were fed the control diet containing 8 ppm Na2SeO3 or 10 ppm of each o-, m-, and p-methoxy BSC and DDS equivalent to 4.1 ppm Se or 20 ppm p-XSC (10 ppm Se) 2 weeks prior to carcinogen (AOM, 15 mg/kg body wt., once weekly for 2 weeks) administration and during and until 8 weeks after AOM treatment. Vehicle-control animals received an equal volume of normal saline. One hour prior to sacrifice, all animals were injected with bromodeoxyuridine (BrdU, 20 mg/kg body wt.). Administration of o-, m-, and p-methoxy BSC, p-XSC, DDS, and Na2SeO3 resulted in decreased colonic labeling index in animal treated with AOM compared to control diet. Notably, p-XSC and Na2SeO3, which showed previously colon tumor inhibitory activity in preclinical efficacy study, were also effective in the present study. The results of our previous and current studies indicate that structurally modified synthetic organoselenium compounds may have great potential as chemopreventive agents.

Sodium cyanate: from a promising therapeutic agent to a research tool in high altitude physiology

Sodium cyanate (NaOCN) first appeared on the biomedical scene as a potential therapeutic agent for sickle-cell disease. Although it did not fulfill its early promise in the clinic, it proved to be useful as a pharmacological tool in physiological research, particularly in the physiology of oxygen transport. NaOCN has been especially valuable in the area of investigation which is reviewed here: the study of oxygen transport, both in normoxic and in hypoxic conditions, in experimental models in which NaOCN was used to induce a shift to the left of the oxygen dissociation curve. The classical idea is that a low Hb-O2 affinity is of adaptive value for life at high altitudes but it has been challenged by several pieces of evidence. One of them is the demonstration of increased survival in hypoxic hypoxia of animals with a high Hb-O2 affinity induced by NaOCN. We also discuss the advantages and potentially confounding factors which should be taken into consideration when interpreting results of studies in which the oxygen dissociation curve has been modified by administration of NaOCN

Cancer chemoprevention by aliphatic selenocyanates: effect of chain length on inhibition of mammary tumors and DMBA adducts.

The objective of this study was to examine the anticarcinogenic activity of a series of aliphatic selenocyanates with increasing length of the carbon side chain, CH3-(CH2)n-SeCN, in which n = 0, 2, 4 or 6. Their ability to prevent mammary cancer was evaluated during the initiation phase using the rat 7,12-dimethyl-benz[a]anthracene (DMBA) model. Each compound was added to the diet at a final concentration of 2 p.p.m. Se and was given from 2 weeks before to 1 week after DMBA administration. Analysis of the tumor data suggested the following order of chemopreventive potency for this series of aliphatic selenocyanates: heptyl approximately pentyl > propyl > methyl. Thus it appears that the length of the carbon side chain is a determinant in modulating the efficacy of these selenium homologs. In vivo results of total DMBA binding and adduct formation in the mammary cells showed a similar trend of progressive reductions following treatment by selenocyanates with increasing length of the alkyl side chain. These studies strongly indicate that aliphatic selenocyanates are effective blocking agents in the DMBA model and are capable of modulating events in the initiation phase of mammary carcinogenesis.

Comparative effect of inorganic and organic selenocyanate derivatives in mammary cancer chemoprevention.

Recently El-Bayoumy and coworkers have reported that 1,4-phenylene-bis(methylene)selenocyanate (p-XSC) was very effective in inhibiting 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis and adduct formation during the initiation phase (Cancer Res., 52, 2402-2407, 1992). Furthermore, this compound was found to be well tolerated by rats at high doses. The present study was designed to extend these earlier observations by investigating the response to lower levels of p-XSC given either before or after DMBA administration. At a level of 15 p.p.m. Se, p-XSC suppressed total mammary tumor yield by 80% and 52% in the initiation phase and post-initiation phase, respectively. A dose-response effect was evident in the range 5-15 p.p.m. Se. When p-XSC was given at a level of 5 p.p.m. Se during the entire course of the experimental period, total tumor yield was reduced by half. This dose is about 4 x less than the maximum tolerable dose (MTD). Other selenocyanate analogs were also examined in an attempt to obtain information on their respective chemopreventive index, which is calculated as the ratio of MTD to the effective dose which produces approximately a 50% inhibition in total tumor yield (ED50). The reagents studied included potassium selenocyanate, methyl selenocyanate and benzyl selenocyanate, as well as sodium selenite (reference compound). Compared to p-XSC, which has a chemopreventive index of 4.0, the other four compounds have a lower index ranging from 1.3 for sodium selenite and potassium selenocyanate to 2.0 for methyl selenocyanate and 2.5 for benzyl selenocyanate. A high chemopreventive index signifies that a compound is well tolerated at doses required for cancer suppression. The last component of the present study involved the repletion assay of liver glutathione peroxidase in selenium-deficient rats as a biomarker to estimate the metabolizability of the above selenium compounds. The bioavailability data suggest that the selenium from p-XSC is not as efficiently incorporated into glutathione peroxidase as the selenium from selenite or the other selenocyanate analogs. Currently, we are working under the hypothesis that the chemical structure of the RSeCN compound could affect activity per se and also influence the rate of release of selenium from the parent compound, thereby impacting on the anticarcinogenic efficacy, tolerance and bioavailability of the compound.

Alteration of the systemic antitumor activity of melphalan by sodium cyanate in MOPC-460D myeloma-bearing BALB/c mice.

Sodium cyanate is a selective inhibitor of protein synthesis in a variety of mammalian tumor cells without a corresponding effect on normal tissue of the tumor-bearing animals. In the present study, we investigated the potential role of sodium cyanate in the augmentation of the antitumor activity of melphalan in MOPC-460D myeloma-bearing BALB/c mice. The simultaneous intraperitoneal injection of sodium cyanate, 250 mg/kg, and melphalan, 12 mg/kg, followed by another dose of sodium cyanate, 200 mg/kg, administered 18 hours later, resulted in a tumor growth inhibition index (TGII) of 207%. In contrast, melphalan or sodium cyanate administered separately at the same dose induced a TGII of 133% and 15%, respectively, when compared to control animals. Furthermore, a direct comparison of the volume of tumor implants in mice treated with the combination of sodium cyanate and melphalan vs. those treated with melphalan alone showed a statistically significant growth inhibition in favor of the sodium cyanate and melphalan combination on days 35, 39, and 42 from initiation of treatment. The data presented here suggest that the antitumor activity of melphalan could be increased, with moderate toxicity, by the concomitant intraperitoneal administration of sodium cyanate in BALB/c mice bearing measurable subcutaneous MOPC-460D tumor transplants. This is the first report of an increase in melphalan antitumor activity by sodium cyanate at a tumor location distant from the site of injection.

Inhibition by dietary benzylselenocyanate of hepatocarcinogenesis induced by azoxymethane in Fischer 344 rats.

The effect of dietary benzylselenocyanate (BSC), a novel organoselenium compound and its sulfur analog, benzylthiocyanate (BTC), on hepatocarcinogenesis induced by azoxymethane (AOM) was investigated in male F344 rats. Eighty-one weanling rats were divided into 3 groups and were raised on a semipurified diet (control diet). Starting from 5 weeks of age, groups of animals consuming the control diet were fed one of the experimental diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 weeks of age, animals were given weekly sc injections of AOM (15 mg/kg body weight once weekly for 2 weeks). One week after the second AOM injection, those groups receiving BSC and BTC diets were transferred to the control diet and continued on this diet until termination of the experiment at 34 weeks after the last AOM injection. For quantitative analysis of enzyme-altered liver cell foci, glutathione S-transferase placental form was stained by an immunohistochemical technique. The results indicate that the incidence and the density of the enzyme-altered foci were significantly lower in AOM-treated rats fed the diet containing 25 ppm BSC (foci incidence 56%, foci density 2.43/cm2) than in AOM-treated animals fed the control diet (foci incidence 92%, foci density 4.79/cm2). The incidence of small altered foci was significantly inhibited in rats fed the BTC diet (35%) as compared to those fed the control diet (68%), but the degree of inhibition was more pronounced in animals fed the BSC diet than in those fed the BTC diet.

Boron neutron capture therapy: linkage of a boronated macromolecule to monoclonal antibodies directed against tumor-associated antigens.

Two new protein-binding polyhedral boron derivatives, isocyanatoundecahydro-closo-dodecaborate(2-) (1) and isocyanato(trimethylamino)octahydro-closo-decaborate(1 -) (2), were synthesized. These anionic isocyanates have long hydrolysis half-lives at pH 7 and react readily with primary or secondary aliphatic amines resulting in spontaneous urea linkage. Utilizing 1, 1100 boron atoms (7.3% boron by weight) were incorporated per molecule of a polyclonal antibody directed against human thymocytes (anti-thymocyte globulin) without denaturation. However, immunoreactivity of the conjugates was lost. Reaction of 1 and 2 with polylysine yielded boronated macromolecules containing 21-28% boron by weight (up to 2000 boron atoms per molecule). Polylysine boronated with 2 was successfully linked to antibody molecules employing the heterobifunctional linking molecules N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) and m-maleimidobenzoyl sulfosuccinimide ester (sulfo-MBS). Separation of the conjugated antibody from the free boronated macromolecules and unconjugated antibody molecules has been achieved by gel filtration on a Sephacryl S-300 column. By linking boronated polylysine to antibodies, greater than 10(3) boron atoms were incorporated with the attachment of this species to one or more sites on the antibody molecule. The resulting immunoconjugates contained greater than 10(3) boron atoms per molecule, retained their immunoreactivity, and potentially might be useful for the selective delivery of large numbers of boron atoms to tumor cells.

[Cosmetic cranioplasty using the bone chips and Biobond (EDH-adhesive): technical note].

A new and simple cosmetic procedure for the prevention of skin depression produced by burr-holes was presented. A mixture of the bone chips obtained at craniotomy and Biobond in a volume ratio of 7:3 was used to fill the bone defect of the burr-holes in 65 cases. The postoperative appearance was excellent cosmetically. This mixture had good plasticity, and could be formed into any irregular shape desired, and there was no increase in the incidence of infectious complications.

Chemoprevention of colon carcinogenesis by dietary organoselenium, benzylselenocyanate, in F344 rats.

The effect of feeding benzylselenocyanate (BSC) and its sulfur analogue, benzylthiocyanate (BTC), 2 wk before, during, and until 1 wk after carcinogen administration (initiation phase) on intestinal carcinogenesis induced by azoxymethane (CAS:25843-45-2) was studied in male F344 rats. Weanling rats were raised on a semipurified diet (AIN-76A diet; control diet). Beginning at 5 wk of age, groups of animals consuming the control diet were fed one of the diets containing 25 ppm BSC or BTC. An additional group was continued on the control diet. At 7 wk of age, all animals in 3 groups, except the vehicle-treated controls, were administered s.c. injections of azoxymethane (15 mg/kg body weight, once weekly for 2 wk). Animals were continued on the control diet and BSC and BTC diets until 1 wk after carcinogen treatment, when those groups receiving BSC and BTC diets were fed the control diet until termination of the experiment. Tissue and blood plasma glutathione peroxidase activity was measured in vehicle-treated animals fed the control diet and BSC and BTC diets for 5 wk. The results indicate that body weights were comparable among the various dietary groups. BSC in the diet significantly inhibited the incidence (percentage of animals with tumors) and multiplicity (tumors/animal) of adenocarcinomas in the colon and multiplicity of adenocarcinomas in the small intestine compared to those fed the control diet. BTC in the diet had no effect on colon and small intestinal tumors. Selenium-dependent glutathione peroxidase activity was significantly increased in kidneys and colon and small intestinal mucosae of animals fed the BSC diet compared to animals fed the BTC and control diets.

Effects of sodium cyanate in mice bearing B16 melanoma.

Sodium cyanate injected IP at a dose level of 200 or 250 mg/kg caused a 90% or greater inhibition of the incorporation of [3H]thymidine into DNA of B16 melanoma transplanted SC in mice. Despite the inhibitory effect of sodium cyanate on precursor incorporation into DNA, no significant effect on host survival was observed when sodium cyanate was administered as a single agent in the diet, in drinking water, or by IP injection to mice that had received IP transplants of B16 melanoma. The action of melphalan and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in prolonging the survival time of melanoma-bearing mice was not enhanced by combined treatment with sodium cyanate. However, combined injections of sodium cyanate and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) increased the survival of tumor-bearing mice significantly more than injections of BCNU alone at a lower dose than the maximum tolerated one. These data and other studies suggest that B16 melanoma may be less responsive to the action of sodium cyanate than are murine leukemic cells or rat hepatomas.

Phase-I clinical trial of sodium cyanate in patients with advanced colorectal carcinoma.

Sodium cyanate, a drug that selectively suppresses amino acid incorporation for protein synthesis in tumor tissue, was given to patients with advanced colorectal carcinoma who had failed to conventional therapy, with the purpose of assessing a maximum tolerable oral dose. At 35 mg/kg p.o. daily, the drug had to be stopped in approximately half (4) of the patients because of gastrointestinal toxicity (nausea, vomiting) and neurologic toxicity (hallucinations, disorientation). However, in 5 other patients, at the same dose, the drug was well tolerated for up to 147 days and for a total cumulative dose of 308 g. In this group of patients, sodium cyanate was stopped because of evidence of tumor progression. No hematologic toxicity was observed. We observed no therapeutic effects. We therefore recommend a starting dose of 30 mg/kg p.o. if a phase-II study is considered.

Effect of administration of sodium cyanate and melphalan on the lifespan of P388 tumor-bearing CD2F1 mice.

Sodium cyanate (NaOCN) at a dose of 250 mg/kg was shown to decrease protein synthesis in P388 leukemia tumor cells to approximately 52% of control values at 2 h and 32% at 5 h after NaOCN administration, without a corresponding decrease in various normal tissues of the tumor-bearing CD2Fl mice. CD2Fl mice that had received P388 tumor cells IP 1 day prior to drug administration underwent various schedules of treatment with NaOCN and melphalan (MLN). NaOCN (200 mg/kg or 250 mg/kg) administered IP has no significant antitumor activity (increased mean lifespan [ILS] less than 20%). The simultaneous IP administration of NaOCN (250 mg/kg) plus MLN (15 mg/kg) resulted in a significantly greater antitumor activity (approximately 265% of control, with 21 of 30 animals being long-term survivors) than MLN (15 mg/kg) alone (approximately 156% of control, with 11 of 30 animals being long-term survivors). This synergism was not observed when MLN was administered 4 h after NaOCN administration. The synergistic activity of MLN with NaOCN does not appear to be secondary to alterations in the absorption from the peritoneal cavity into the systemic circulation as determined by 3H2O. NaOCN does not increase the intracellular concentration of [chloroethyl-14C]MLN into P388 cells. The mechanism of the synergistic antitumor activity of simultaneous IP administration of NaOCN and MLN is unknown.

Comparative evaluation of fifteen anti-sickling agents.

Fifteen compounds reported to be inhibitors of gelation or sickling were studied by standard methods. These tests included (1) the determination of the solubility of deoxyhemoglobin S or Csat, (2) evaluation of sickling in whole SS blood at various pO2s, (3) measurement of the oxygen affinity of hemoglobin and blood, and (4) examination of red cell indices and morphology. Among the 4 noncovalent agents tested, butylurea was the most potent inhibitor of gelation and sickling in vitro; however, relatively high concentrations were required compared to the covalent agents. In the latter group, bis-(3,5 dibromosalicyl)-fumarate, nitrogen mustard, and dimethyladipimidate were especially effective inhibitors of gelation and/or sickling. All of these compounds require further development before they can be considered for clinical use.

Quantitation of red cell deformability during progressive deoxygenation and oxygenation in sickling disorders (the use of an automated Ektacytometer).

1. The Ektacytometer, which allows quantitation of cell fluidity under known environmental conditions, has been recently modified so that cells can be exposed to any desired O2 tension during shear stress. 2. Heterozygotes (HbAS)show a pO2 vs deformability curve which varies from patient to patient in relation to the quantity of HbS. In the high viscosity medium used for this measurement, erythrocytes are normally deformable at any pO2 from 5 mmHg to normoxic conditions, at physiologic pH [7.3] and osmolarity (290 mOsm Kg-1). Modulation of the pH and osmolarity induces cell rigidity at different pO2 below 40 mmHg. 3. Homozygotes (HbSS) blood contains heterogeneous erythrocyte populations from the reticulocytes to abnormally dense cells (heterogeneity in cell volume, Hb concentration, shape, etc.). After separation by differential centrifugation, the various fractions each show a characteristic response to pO2 changes, pH, osmolarity and other parameters, which are specific to each patient and his pathological status at a given time. 4. This method was used to evaluate the activity of anti-sickling drugs. In addition, the action of such compounds on normal cells gives information on the mechanism of activity (changes in volume, in oxygen affinity, membrane properties or other--yet poorly explored--parameters). 5. This new application of the Ektacytometer may be of value for a) evaluating anti-sickling drugs and designing new therapeutic modalities, b) monitoring therapy of sickle cell patients, and c) research into the phenomenon of sickling.

Measurements of DNA damage in Chinese hamster cells treated with equitoxic and equimutagenic doses of nitrosoureas.

The DNA of V-79 Chinese hamster cells was examined by alkaline elution following treatment of cultures with eight different nitrosoureas. Drug incubations were performed under consistent biological conditions of equal toxicity and equal mutation induction at the hypoxanthineguanine phosphoribosyltransferase locus. The goals of this study were to determine whether DNA damage could be detected in cells treated with biologically relevant doses of nitrosoureas and to determine whether the type and number of observed DNA lesions could be correlated with the cytotoxic and mutagenic effects of the drugs. All of the compounds tested produced, to some degree, lesions that were observed as DNA strand breaks upon exposure of the DNA to alkali. The levels of DNA strand breaks and/or alkali-labile lesions were comparable for all of the drugs at the equimutagenic doses. DNA cross-linking was observed at both the equitoxic and the equimutagenic concentrations of the haloethylnitrosoureas, but cross-linking was not observed with methylnitrosourea or streptozotocin. Methylnitrosourea and streptozotocin required approximately 40 times the drug concentration to produce toxicity equal to the haloethylnitrosoureas. These data suggest that the ability to cross-link DNA confers increased cytotoxicity to the haloethylnitrosoureas.

Iron metabolism, sickle cell disease, and response to cyanate.

In an attempt to understand the variability of the hematologic response to oral sodium cyanate, iron metabolism was studied in a group of 39 patients with sickel cell disease. Eleven of the 39 patients were found to have no stainable iron in the marrow despite the fact that patients with sickle cell disease are generally considered to have hemosiderosis. The mean per cent saturation and total iron-binding capacity were in the low-normal range in sickle cell patients whether or not stainable iron was present in the bone marrow aspirate. Serum ferritin concentrations, on the other hand, were found to be high in both groups (greater than 500 mu g/liter) when compared to controls (60 mu g/liter). The high serum ferritin levels denoted significant total-body iron deposition which may be unavailable for normal metabolic processes. One patient with no stainable iron in the bone marrow aspirate did respond to iron therapy alone with an increase in hemoglobin concentration. Serum ceruloplasmin levels were also found to be high in sickle cell disease patients. The ability to respond to oral cyanate therapy was correlated with the amount of stainable iron in the bone marrow aspirate. These studies emphasize the necessity of a reevaluation of iron metabolism in the pathophysiology and treatment of sickle cell disease.