The Synthesis of a New Class of Highly Fluorescent Chromones via an Inverse-Demand Hetero-Diels-Alder Reaction

A new class of fluorophores has been developed utilizing an inverse-demand hetero-Diels-Alder reaction with silyl enol ethers and substituted 3-formylchromones. These compounds yield blue to green fluorescence with quantum yields up to 73%. They also exhibit good potential for use as fluorescent probes in biological systems, as they are cell membrane permeable with low cytotoxicity.

Efficacy of the saponin component of Impatiens capensis Meerb.in preventing urushiol-induced contact dermatitis

ETHNOPHARMACOLOGICAL RELEVANCE

Many different tribes of American Indians used jewelweed, Impatiens capensis Meerb, as a plant mash to reduce development of poison ivy dermatitis. Saponins are a natural soapy constituent found within plants. A 2012 study suggested that saponins may be present in jewelweed which could be responsible for its efficacy in preventing rash development following contact with Toxicodendron radicans (L.) Kuntze (poison ivy). This study validated this hypothesis and demonstrated additional biological activity of the jewelweed saponin containing extract.

MATERIALS AND METHODS

Fresh I. capensis leaves were extracted with methanol and further partitioned between ethyl acetate and water, with a final separation between water and n-butanol, to obtain a saponin containing extract. The presence of saponins in the extract was demonstrated by the observation of foaming and using a vanillin colorimetric assay for total saponins. Efficacy of the saponin containing extracts in rash reduction was tested by brushing poison ivy (PI) onto the forearms of volunteers (N=23) in six locations and treating these PI exposed areas with distilled water (control), saponin containing extracts, fresh plant mashes, and soaps made with and without plant extracts. Saponin containing extracts were further tested for biological activity against both gram negative and gram positive bacteria and against cancer cell lines A-375, HT-29, and MCF-7. Additionally, because saponins have been shown to have a stimulatory effect in cardiac muscle 2 µl saponin extract was applied superficially to black worms, Lumbriculus variegatus (N=5).

RESULTS, AND CONCLUSIONS

Both saponin containing extracts and all soaps tested were effective in reducing poison ivy dermatitis; thus, saponin content correlates with PI rash prevention. No apparent antibiosis was observed against any bacteria tested; however, dose response cytotoxicity was documented against MCF-7 breast cancer cells and cytostatic activity was seen against the HT-29 colon cancer cell lines. Lumbriculus variegatus exhibited a 138% increase in heart rate over baseline rate five minutes post treatment implying a possible positive chronotropic effect.

A comprehensive ligand based mapping of the σ₂ receptor binding pocket

The sigma (σ) receptor system consists of at least two major receptor subtypes: σ₁ and σ₂. Several potential therapeutic applications would benefit from structural knowledge of the σ₂ receptor but gaining this knowledge has been hampered by the difficulties associated with its isolation and, thus, characterization. Here, a ligand based approach has been adopted using the program PHASE® and a group of 41 potent and structurally diverse σ₂ ligands to develop several pharmacophore models for different families of σ₂ ligands. These pharmacophores were analyzed to identify the different binding modes to the receptor and were combined together to construct a comprehensive pharmacophore that was used to develop a structural model for the σ₂ binding pocket. A total of six binding modes were identified and could be classified as neutral or charged modes. The results presented here also indicate the significance of hydrophobic interactions to σ₂ binding and the requirement of hydrogen bonding interactions to increase the affinity for this receptor subtype. This work adds breadth to our knowledge of this receptor's binding site, and should contribute significantly to the development of novel selective σ₂ ligands.

The effectiveness of jewelweed, Impatiens capensis, the related cultivar I. balsamina and the component, lawsone in preventing post poison ivy exposure contact dermatitis

ETHNOPHARMACOLOGICAL RELEVANCE

Impatiens capensis (jewelweed) is native to the Eastern and Midwestern US and Canada. Many Native American tribes used I. capensis and its close relatives to treat/prevent rash from plant sources particularly Toxicodendron radicans and Urtica dioica. I. balsamina (garden balsam) a native of China was used by the indigenous people of Asia for similar purposes.

AIM OF STUDY

This study aims to validate ethnopharmacological use of jewelweed in poison ivy (PI) dermatitis prevention and to refute scientific papers denying this efficacy. Additionally, the content of lawsone, the purported effective agent in jewelweed preparations, was measured to see if its concentration correlated with jewelweed preparation efficacy.

MATERIAL AND METHODS

Poison ivy was brushed onto forearms of volunteers in 6 locations and exposed areas were treated with jewelweed extracts, fresh plant mashes, soaps made of plant extracts, water and Dawn® dish soap. Rash development was scored on a scale of 0-14.

RESULTS

Jewelweed mash was effective in reducing poison ivy dermatitis, supporting ethnobotanical use. However, jewelweed extracts were not effective; and soaps made of these extracts were effective but no more so than jewelweed-free soaps. Lawsone content varied with harvest season and did not appear to affect rash development.

CONCLUSION

Jewelweed is an efficacious plant for preventing development of dermatitis following poison ivy contact, but soap is more effective. Lawsone content does not correlate with PI rash prevention. Perhaps saponins, the soapy component of jewelweed are the effective agents.

Abstract 4297: Morphology of MCF-7 colonies formed in agarose cell culture

Previously, we demonstrated that the MCF-7 cell line grows in a permissive 3-D agarose culture (Kinder and Aulthouse, Cancer Letters., 2004, 205(1), 49-53). Single cells form colonies over time; thus, mitotic activity can be monitored in response to various agents. We studied the morphology of the colonies that formed following growth from single cells at 3 time points: 1.5, 2, 2.5 weeks. The MCF-7 cells grew into clusters (solid) and hollow tube-like structures. These structures were confirmed by H&E stained serial sections of paraffin embedded cultures. H&E staining also revealed abundant mitotic figures. Because calcium foci are common in breast cancers, we also evaluated the cultures for calcium expression using the von Kossa reaction. Placenta was used as a control. At all time points, calcium was detected, but no particular pattern was noted in the calcium distribution between the clusters and the hollow tube-like structures. With morphology and calcium expression described, we further examined cell growth inhibition and cytotoxicity of estradiol and tamoxifen on the MCF-7 cells. Added estradiol enhanced the growth of the cells, while tamoxifen was cytostatic at concentrations below 1.3 × 10-4 nM. At high tamoxifen concentrations (>2 × 10-4 nM) cytotoxicity was noted. This was likely due to sigma-2 receptor binding rather than estrogen receptor blocking. Combination of estradiol with tamoxifen had a more pronounced effect on the cytotoxicity caused by tamoxifen. These morphological and mechanistic findings support the use of this model for studying the MCF-7 cell line in agarose culture.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4297. doi:10.1158/1538-7445.AM2011-4297

Computational strategies for the development of novel small molecule rheumatoid arthritis therapies

Rheumatoid arthritis is a chronic autoimmune disorder that causes joint disfigurement and destruction leading to reduced quality of life. Effective drug therapies include the Disease Modifying Anti-Rheumatic Drugs which can help impede the progression of the disease but are not always effective. It is, therefore important to identify novel and effective therapies to combat this debilitating disorder. Several bioinformatics tools and computational approaches can be utilized to identify novel and effective therapies for rheumatoid arthritis and these are presented here.

Abstract 737: Modeling of σ2 selective agonists for the development of new anticancer agents that utilize the celecoxib scaffold

Celecoxib has proved to be an enigma as a potential anticancer agent. COX-2 inhibition is not necessarily involved in its mechanism of cytotoxicity, and it induces a non-classical apoptotic pathway leading to cell death in some cell culture models. Because the classical pathways are not always induced by celecoxib, we hypothesized that celecoxib might be working as a σ2 receptor agonist as part of its cytotoxicity. In addition, published research has supported the therapeutic potential of σ2 receptor agonists in cancer chemotherapy. We have determined that celecoxib will inhibit the CRL-1620 cell line with an IC50 of 32 μM, and the 9L rat glioma model with an IC50 of 60 μM. Using a group of 41 high affinity σ2 receptor selective agonists and following a ligand-based drug design approach, we have developed a four-site pharmacophore model for σ2 receptor agonists. Upon aligning celecoxib to this model, it matched three of the four sites, further supporting our hypothesis that celecoxib might be working as a σ2 receptor agonist as part of its cytotoxicity. Additional compounds have been developed utilizing the celecoxib scaffold as σ2 receptor agonist anticancer agents. From the pharmacophore model we also developed an in silico model for the σ2 receptor binding pocket as it has not been cloned nor has its three dimensional structure been determined.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 737.

The hallucinogen derived from Salvia divinorum, salvinorin A, has kappa-opioid agonist discriminative stimulus effects in rats

Data from clinical and preclinical studies converge implicating the plant-derived hallucinogen salvinorin A as an important pharmacologic tool; this psychoactive compound may expand scientific understandings on mammalian kappa-opioid receptor systems. Human salvinorin A effects, consistent with kappa-opioid receptor agonism, include antinociception, sedation, dysphoria and distorted perceptions. The experiments reported here measured salvinorin A (1-3mg/kg, i.p.) discriminative stimulus properties in male Sprague-Dawley rats conditioned to recognize the discriminative stimulus cue generated by the well characterized kappa-opioid agonist U-69593 (0.56 mg/kg, i.p.). At three distinct active doses, salvinorin A fully substituted for U-69593 without altering response rates. The lever choice pattern in U-69593 trained animals reverted to vehicle lever responding when a kappa selective antagonist compound, nor-BNI (4.5 nM, i.c.v.) was administered 1h prior to salvinorin A, yet nor-BNI alone failed to impact the rate or pattern of subject responses. These findings confirm and extend results published after similar drug discrimination tests were performed in rhesus monkeys. The discussion section of this article highlights public concern over salvinorin A misuse and emphasizes several potential pharmacotherapeutic applications for salvinorin A or analogue compounds.

Effects of extracts of lupine seed on blood glucose levels in glucose resistant mice: antihyperglycemic effects of Lupinus albus (white lupine, Egypt) and Lupinus caudatus (tailcup lupine, Mesa Verde National Park)

Lupine is a medicinal food plant with potential value in the management of diabetes. In white mice, extracts of seeds of the white lupine [Lupinus albus (L. termis L.)] were associated with increased tolerance to an oral glucose bolus. Antihyperglycemic activity was present in extracts of the whole seed but not extracts of the seed coat, and was not detected when glucose was administered intraperitoneally rather than orally. However, in contrast to results seen with the prescription drug, acarbose, lupine extract did not appear to increase the bulk or carbohydrate content of the feces. Antihyperglycemic activity was also seen in extracts of the tailcup lupine (L. caudatus) found in the Four Corners Region of the United States.

Bromophenol blue staining of tumors in a rat glioma model

OBJECTIVE

For patients with gliomas, decreasing the tumor burden with macroscopic surgical resection may affect quality of life, time to tumor progression, and survival. Injection of bromophenol blue (BPB) may enhance intraoperative visualization of an infiltrating tumor and its margins and improve the extent of resection. In this study, we investigated the uptake of BPB in experimental rat brain tumors.

METHODS

We first conducted a toxicity study with bolus intravenous injections of 5, 60, and 360 mg/kg doses of BPB in nontumor-bearing Fischer 344 rats. No adverse effects were observed in any of the animals during the 60 day observation period. We then injected 9L tumor cells intracerebrally into Fischer 344 rats and approximately 2 weeks later, administered a bolus intravenous injection of 5 to 360 mg/kg BPB. Fifteen minutes after BPB injection, we sacrificed the animals and removed their brains. In a subsequent study, we injected 180 mg/kg BPB and sacrificed animals at several time points to monitor tumor staining over time.

RESULTS

The stain was clearly visible and localized to the tumor for all BPB concentrations 60 mg/kg or greater, and in an additional experiment, we found that tumor staining persisted for at least 8 hours after BPB injection.

CONCLUSION

We conclude that BPB helped visualize experimental tumors at time points from a few minutes to several hours after injection. Because BPB also proved to be nontoxic to the animals at effective concentrations, we believe the compound may be potentially useful in helping neurosurgeons visualize brain tumors in humans.

MCF-7 breast cancer cell line grown in agarose culture for study of COX-2 inhibitors in three-dimensional growth system

Herein we report a method for studying slow acting pharmaceutical COX-2 inhibitors in the MCF-7 breast cancer cell line where cells are grown in a three-dimensional format within an agarose matrix. The cancer cells are suspended in agarose and plated in a cell culture dish, where they will form small multicellular 'tumors' in the agarose. The time frame for conducting experiments is up to 2.5 weeks, and gives ample time for COX-2 inhibitors to induce cell death. Etodolac was used for these experiments, and was found to induce cell death in a time dependent manner over a 2.5-week period. This is in contrast to the cell line grown in monolayer and treated with the same concentrations of etodolac. This method is appropriate for determining mechanisms of cell death caused by COX-2 inhibition.

In vivo microdialysis and conditioned place preference studies in rats are consistent with abuse potential of tramadol

The abuse potential of tramadol was investigated using both in vivo microdialysis measures of dopamine (DA) release within the nucleus accumbens (NAc) shell and the conditioned place preference (CPP) paradigm in rats. Tramadol (75 mg/kg, i.p.) induced a statistically significant increase (starting 80 min posttreatment) in DA release within the NAc shell, which was maintained for at least 120 min posttreatment. Tramadol (18.75, 37.5, and 75 mg/kg i.p.) produced a statistically significant CPP, with the effects of the two highest doses comparable to those induced by morphine (5 mg/kg, s.c.). The release of DA within the NAc shell may be responsible for the rewarding properties of tramadol and, together with the CPP results, provide evidence that tramadol may possess greater abuse potential than originally believed.

Bcl-2-mediated resistance to apoptosis is associated with glutathione-induced inhibition of AP24 activation of nuclear DNA fragmentation

Studies on the mechanism of apoptosis in this laboratory support a model in which signal transduction involving caspase 3 leads to activation of a serine protease called Mr 24,000 apoptotic protease (AP24), which then induces internucleosomal DNA fragmentation in the nucleus. This study examined the effect of Bcl-2 overexpression on activation of AP24 and the induction of DNA fragmentation by AP24 in isolated nuclei. It was demonstrated that overexpression of Bcl-2 in either HL-60 or PW leukemia cell lines suppressed activation of AP24 induced by either tumor necrosis factor or UV light and protected cells from apoptosis. Furthermore, nuclei isolated from Bcl-2-overexpressing cells were relatively resistant to internucleosomal DNA fragmentation induced by AP24 isolated from apoptotic cells. Bcl-2-overexpressing cells that were nutritionally depleted of glutathione (GSH) became sensitive to tumor necrosis factor- or UV light-induced activation of AP24 and underwent apoptotic cell death. Moreover, nuclei isolated from Bcl-2-overexpressing cells that were depleted of GSH became sensitive to AP24-induced DNA fragmentation. The addition of exogenous GSH blocked the proteolytic activity of AP24, as well as its ability to induce DNA fragmentation in normal isolated nuclei. These results indicate that Bcl-2 can attenuate at least two events in the AP24 apoptotic pathway: activation of AP24 and induction of DNA fragmentation by activated AP24. Furthermore, agents that deplete intracellular levels of GSH may have therapeutic use in the sensitization of Bcl-2-overexpressing cancer cells to apoptotic cell death.

Chemotherapeutic drug activation of the AP24 protease in apoptosis: requirement for caspase 3-like-proteases

AP24 is a serine protease that is activated during TNF or UV light-induced apoptosis and stimulates DNA fragmentation in isolated nuclei. The present study determined whether apoptosis induced by chemotherapeutic drugs resulted in activation of AP24 and examined the possible relationship to caspase activity. We showed that an inhibitor of AP24, DK120, could block DNA fragmentation induced in three leukemia cell lines (U937, HL-60, and CEM) by various DNA-damaging drugs including etoposide, camptothecin, chlorambucil, and the CC1065-related drug, YW201. Etoposide-induced activation of intracellular DEVD-pNa cleaving activity and apoptosis was suppressed by low micromolar concentrations of cell-permeable inhibitors of caspase-3. Furthermore, these inhibitors also suppressed activation of AP24. In contrast, DK120 did not prevent etoposide activation of DEVD-pNa cleaving activity, nor did it prevent cleavage of poly(ADP-ribose) polymerase. AP24 isolated from apoptotic cells following treatment with etoposide activated DNA fragmentation in isolated normal nuclei and was inhibited by DK120, but not by caspase inhibitors. This evidence shows that activation of caspase 3-like proteases generates signals that contribute to the activation of AP24 which may then induce nuclear DNA fragmentation in chemotherapeutic drug-induced apoptosis.

Activation of CPP32-like proteases is not sufficient to trigger apoptosis: inhibition of apoptosis by agents that suppress activation of AP24, but not CPP32-like activity

The 24-kD apoptotic protease (AP24) is a serine protease that is activated during apoptosis and has the capacity to activate internucleosomal DNA fragmentation in isolated nuclei. This study examined the following: (a) the functional relationship between AP24 and the CPP32-like proteases of the caspase family; and (b) whether activation of CPP32-like proteases is sufficient to commit irreversibly a cell to apoptotic death. In three different leukemia cell lines, we showed that agents that directly (carbobenzoxy-Ala-Ala-borophe (DK120) or indirectly inhibit activation of AP24 (protein kinase inhibitors, basic fibroblast growth factor, tosylphenylalaninechloromethylketone, and caspase inhibitors) protected cells from apoptosis induced by TNF or UV light. Only the caspase inhibitors, however, prevented activation of CPP32-like activity as revealed by cleavage of the synthetic substrate, DEVD-pNa, by cell cytosols, and also by in vivo cleavage of poly (ADP-ribosyl) polymerase, a known substrate of CPP32. Activation of DEVD-pNa cleaving activity without apoptosis was also demonstrated in two variants derived from the U937 monocytic leukemia in the absence of exogenous inhibitors. Cell-permeable peptide inhibitors selective for CPP32-like proteases suppressed AP24 activation and apoptotic death. These findings indicate that CPP32-like activity is one of several upstream signals required for AP24 activation. Furthermore, activation of CPP32-like proteases alone is not sufficient to commit irreversibly a cell to apoptotic death under conditions where activation of AP24 is inhibited.

Solid-phase synthesis of hydroxyethylamine angiotensin analogues

Three hydroxyethylamine analogues of angiotensins II, III, and IV were prepared by solid-phase methods. The resin-bound peptide was alkylated with the iodomethylketone derivative of the N-terminal amino acid, followed by reduction to the alcohol using sodium borohydride. The iodomethylketones can be made in good yields from commercially available N-protected amino acids. The compounds were evaluated for their ability to displace labeled angiotensins from bovine adrenal membranes, and their metabolic stability tested in kidney homogenates and aminopeptidase M preparations. The hydroxyethylamine amide bond replacement reduced the affinity of the analogues; however, they were substantially more stable to enzymatic degradation.

Haloacetate-induced oxidative damage to DNA in the liver of male B6C3F1 mice

Brominated and chlorinated haloacetates (HAs) are by-products of drinking water disinfection. Dichloroacetate (DCA) and trichloroacetate (TCA) are hepatocarcinogenic in rodents, but the brominated analogs have received little study. Prior work has indicated that acute doses of the brominated derivatives are more potent inducers of oxidative stress and increase the 8-hydroxydeoxyguanosine (8-OH-dG) content of the nuclear DNA in the liver. Since, DCA and TCA are also known as weak peroxisome proliferators, the present study was intended to determine whether this activity might be exacerbated by peroxisomal proliferation. Classical responses to peroxisome proliferators, cyanide-insensitive acyl-CoA oxidase activity and increased 12-hydroxylation of lauric acid, were elevated in a dose-related manner in mice maintained on TCA and clofibric acid (positive control), but not with DCA, dibromoacetate (DBA) or bromochloroacetate (BCA). Administration of the HAs in drinking water to male B6C3F1 mice for periods from 3 to 10 weeks resulted in dose-related increases in 8-OH-dG in nuclear DNA of the liver with DBA and BCA, but not with TCA or DCA. These findings indicate that oxidative damage induced by the haloacetates is, at least in part, independent of peroxisome proliferation. In addition, these data suggest that oxidative damage to DNA may play a more important role in the chronic toxicology of brominated compared to the chlorinated haloacetates.

Lipid peroxidation and formation of 8-hydroxydeoxyguanosine from acute doses of halogenated acetic acids

Chlorinated, brominated, and mixed bromochloro acetates are major by-products of water disinfection by chlorine or ozone. The chlorinated acetates, trichloroacetate (TCA) and dichioroacetate (DCA), are carcinogenic in rodents. Brominated analogs of TCA and DCA have received little study. TCA and DCA induce lipid peroxidation in the livers of rodents when administered acutely. Oxidative stress can also result in oxidative damage to DNA, most commonly measured as increases in 8-hydroxydeoxyguanosine (8-OHdG) adducts. In this study, the ability of acute doses of TCA, DCA, dibromoacetate (DBA), bromodichloroacetate (BDCA), and bromochloroacetate (BCA) to induce lipid peroxidation and 8-OHdG formation was examined. Male B6C3F1 mice developed significant increases in 8-OHdG/dG ratios in nuclear DNA isolated from livers when treated with haloacetates. The extent of 8-OHdG formation appeared to be related to the ability to induce thiobarbituric acid-reactive substances (TBARS). The order of potency was DBA = BCA > BDCA > DCA > TCA. The induction of 8-OHdG was found to be generally more sensitive to treatment with haloacetates than the TBARS response. Significantly elevated levels of 8-OHdG were observed at doses of DBA, BCA, and BDCA as low as 30 mg/kg. We suggest that formation of 8-OHdG by brominated haloacetates may contribute to their toxicological effects.

Biochemical pathways of apoptosis: nicotinamide adenine dinucleotide-deficient cells are resistant to tumor necrosis factor or ultraviolet light activation of the 24-kD apoptotic protease and DNA fragmentation

The function of nicotinamide adenine dinucleotide (NAD) and adenosine diphosphate (ADP) ribosylation reactions in the mechanism of apoptotic cell death is controversial, although one theory postulates an essential role for NAD depletion by poly-ADP-ribose polymerase. The present study examined the role of intracellular NAD in tumor necrosis factor (TNF) and ultraviolet (UV) light-induced activation of the 24-kD apoptotic protease (AP24) leading to internucleosomal DNA fragmentation and death. Our results demonstrate that nutritional depletion of NAD to undetectable levels in two leukemia lines (U937 and HL-60) renders them completely resistant to apoptosis. This was attributed to a block in the activation of AP24 and subsequent DNA cleavage. Normal cells show an elevation of ADP-ribosyl transferase (ADPRT) in both the cytosol and nucleus after exposure to TNF, but before DNA fragmentation. ADPRT activity as well as cell death was suppressed by an inhibitor specific for mono-ADPRT. Nuclei from NAD-depleted cells were still sensitive to DNA fragmentation induced by exogenous AP24, indicating a selective function for NAD upstream of AP24 activation in the apoptotic pathway. We confirmed a requirement for intracellular NAD, activation of ADPRT, and subsequent NAD depletion during apoptosis in KG1a, YAC-1, and BW1547 leukemia cell lines. However, this mechanism is not universal, since BJAB and Jurkat leukemia cells underwent apoptosis normally, even in the absence of detectable intracellular NAD. We conclude that TNF or UV light-induced apoptotic cell death is not due to NAD depletion in some leukemia cell lines. Rather, NAD-dependent reactions which may involve mono-ADPRT, function in signal transduction leading to activation of AP24, with subsequent DNA fragmentation and cell death.

Purification of a 24-kD protease from apoptotic tumor cells that activates DNA fragmentation

We report the purification of a protease from tumor cells undergoing apoptosis that is involved in activating DNA fragmentation. Initial studies revealed that two inhibitors of serine proteases, N-1-tosylamide-2-phenylethylchloromethyl ketone and carbobenzoxy-Ala-Ala-borophe (DK120), suppressed tumor necrosis factor or ultraviolet (UV) light-induced DNA fragmentation in the U937 histiocytic lymphoma as well as UV light-induced DNA fragmentation in the BT-20 breast carcinoma, HL-60 myelocytic leukemia, and 3T3 fibroblasts. The protease was purified by affinity chromatography with DK120 as ligand and showed high activity on a synthetic substrate preferred by elastase-like enzymes (Ala-Ala-Pro-Val p-nitroanilide), but was inactive on the trypsin substrate, N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester, or the chymotrypsin substrate, Ala-Ala-Pro-Phe p-nitroanilide. The activity of the DK120-binding protease purified from U937 cells undergoing apoptosis was increased approximately 10-fold over that recovered from normal cells. Further purification to homogeneity by heparin-Sepharose affinity chromatography followed by reverse phase high-performance liquid chromatography revealed a single band of 24 kD on a silver-stained sodium dodecyl sulfate gel. In addition to protease activity, the purified enzyme induced DNA fragmentation into multiples of 180 basepairs in isolated U937 nuclei. These findings suggest the 24-kD protease is a novel enzyme that activates DNA fragmentation in U937 cells undergoing apoptosis.

Analogues of carbamyl aspartate as inhibitors of dihydroorotase: preparation of boronic acid transition-state analogues and a zinc chelator carbamylhomocysteine

Dihydroorotase (DHO) catalyzes the conversion of carbamyl aspartate (CA) to dihydroorotate (DO) in the de novo pyrimidine biosynthetic pathway. Few effective inhibitors of DHO have been reported, and thus blockade of this reaction has not been widely pursued as a strategy for development of antitumor agents. Utilizing two mechanism-based strategies, we have designed and prepared potential DHO inhibitor analogues of CA. One strategy replaced the gamma-carboxyl moiety of CA with a boronic acid. This substitution yields compounds which form stable charged tetrahedral intermediates and mimic the enzyme-substrate transition state. Preparation of the boronic acid analogues of CA and its carboxylic acid esters focused on a Curtius rearrangement as a key step following a malonic ester synthesis. This was followed by carbamoylation of the free amine under nonaqueous neutral conditions with Si(NCO)4. The ethyl ester was a competitive inhibitor of DHO with an apparent Ki of 5.07 microM, while the nonesterified analogue and the methyl ester were not effective inhibitors. None of the compounds were cytotoxic against L1210 cells in culture. An active-site-directed sulfhydryl-containing zinc chelator was also prepared. This analogue irreversibly inhibited the enzyme, but it also was ineffective in L1210 growth inhibition.

Preclinical pharmacologic studies of the new antitumor agent carmethizole (NSC-602668) in the mouse and beagle dog

The chemical breakdown of carmethizole [1-methyl-2-methylthio-4,5-bis-(hydroxymethyl)imidazole-4',5'- bis(N-methylcarbamate)hydrochloride] and its pharmacokinetics in the mouse and beagle dog were studied. Carmethizole was relatively unstable in aqueous media, having a half-life of less than or equal to 1 h in 0.9% sodium chloride, human whole blood, human plasma, and dog urine at 37 degrees C. Its major breakdown product in 0.9% sodium chloride and pH 5.0 sodium phosphate buffer was carmethizole diol. When carmethizole was added to pH 7.0 or pH 9.0 sodium phosphate buffer, the major breakdown product was carmethizole diol-4'-monophosphate. Carmethizole reacted directly with glutathione at pH 8.0, forming a glutathione adduct of carmethizole monocarbamate. Elimination of the drug from the plasma of the beagle dog following i.v. bolus doses of 22.4 and 4.3 mg/kg was biphasic. At these doses the terminal half-life was 39 and 46 min, respectively, and the respective total body clearance was 4.6 and 7.7 ml/min per kg. The 22.4 mg/kg dose was lethal to the beagle dog by day 4. Elimination of carmethizole from the plasma of mice following an i.v. bolus dose of 115 mg/kg was monoexponential, with a half-life of 11.6 min and a total body plasma clearance of 43.6 ml/min per kg. When the drug was infused at 230 mg/kg over 8 h into mice, the total body clearance was 40.8 ml/min per kg. Following the i.v. bolus administration of carmethizole to mice, 30% of the total dose was excreted in urine over 3 h as carmethizole diol, 10%, as carmethizole diol-sulfate, 3.4%, as carmethizole 4'-monocarbamate, and 2.4%, as unchanged drug.

Acylamino boronic acids and difluoroborane analogues of amino acids: potent inhibitors of chymotrypsin and elastase

A series of 1-acylamino boronic acids (IA-VA), analogues of the amino acids phenylalanine, phenylglycine, alanine, valine, and isoleucine, were prepared as potential transition-state inhibitors of the serine proteases alpha-chymotrypsin and elastase, by a boronate homologation reaction. The corresponding difluoroboranes (IB-VB), produced from the boronic acids by treatment with HF, were more easily purified than the boronic acids. Since the difluoroboranes readily hydrolyze in water, they proved to be convenient precursors for the boronic acids. The phenylalanine and phenylglycine analogues I and II were good competitive inhibitors of alpha-chymotrypsin (Ki = 0.3-8 microM), and the alanine, valine, and isoleucine analogues (III-IV) proved to be good inhibitors of elastase (Ki = 0.1-35 microM). On the basis of their high affinity and the tendency of boronic acids to form borate complexes, these acylamino boronic acids may be behaving as transition-state inhibitors.

Chemically reactive estrogens: synthesis and estrogen receptor interactions of hexestrol ether derivatives and 4-substituted deoxyhexestrol derivatives bearing alkylating functions

A series of chemically reactive derivatives of the nonsteroidal estrogen hexestrol have been synthesized as potential affinity labels for the estrogen receptor or as cytotoxic agents with selective activity against receptor-containing cells. These compounds are hexestrol ethers with halo ketone, halohydrin, or epoxide functions or 4-substituted deoxyhexestrols with halo ketone, benzyl halide, nitro, azide, sulfonyl fluoride, or sulfonyl azide groups. The alkylating activity of the electrophilic derivatives was measured using the colorimetric reagent nitrobenzylpyridine, the bromo derivatives being considerably more reactive than the chloro ones. Their reversible binding to the lamb uterine estrogen receptor was measured by competitive binding assays, and their irreversible reaction with receptor was measured by exchange assays that determine the rate and extent of receptor inactivation. In general, monoetherification of hexestrol or substitution of deoxyhexestrol produces compounds with relatively low affinity for the estrogen receptor (0.3-10% that of estradiol). Most of the electrophilic derivatives are rapid and effective inactivators of receptor (24-70% inactivation within 0.5-5 h at 25 degrees C). Of the photosensitive derivatives, 4-azidodeoxyhexestrol appears to be the most efficient receptor inactivator (49%). The high reactivity of these compounds toward the estrogen receptor and the lack of interference by their reaction with other cellular nucleophiles suggest that these compounds may be useful as affinity-labeling agents or as selective cytotoxic agents in intact systems.