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M F Stevens

Publications and source records attributed to M F Stevens.

At least 37 records · Page 2Linked to original sources
PubMed1999

Antitumor benzothiazoles. 8. Synthesis, metabolic formation, and biological properties of the C- and N-oxidation products of antitumor 2-(4-aminophenyl)benzothiazoles.

2-(4-Aminophenyl)benzothiazoles 1 and their N-acetylated forms have been converted to C- and N-hydroxylated derivatives to investigate the role of metabolic oxidation in the mode of action of this series of compounds. 2-(4-Amino-3-methylphenyl)benzothiazole (1a, DF 203, NSC 674495) is a novel and potent antitumor agent with selective growth inhibitory properties against human cancer cell lines. Very low IC(50) values (<0.1 microM) were encountered in the most sensitive breast cancer cell lines, MCF-7 and T-47D, whereas renal cell line TK-10 was weakly inhibited by 1a. Cell lines from the same tissue origin, MDA-MB-435 (breast), CAKI-1 (renal), and A498 (renal), were insensitive to 1a. Accumulation and metabolism of 1a were observed in sensitive cell lines only, with the highest rate of metabolism occurring in the most sensitive MCF-7 and T-47D cells. Thus, differential uptake and metabolism of 1a by cancer cell lines may underlie its selective profile of anticancer activity. A major metabolite in these sensitive cell lines has been identified as 2-(4-amino-3-methylphenyl)-6-hydroxybenzothiazole (6c). Hydroxylation of 1a was not detected in the homogenate of previously untreated MCF-7, T-47D, and TK-10 cells but was readily observed in homogenates of sensitive cells that were pretreated with 1a. Accumulation and covalent binding of [(14)C]1a derived radioactivity was observed in the sensitive MCF-7 cell line but not in the insensitive MDA-MB-435 cell line. The mechanism of growth inhibition by 1a, which is unknown, may be dependent on the differential metabolism of the drug to an activated form by sensitive cell lines only and its covalent binding to an intracellular protein. However, the 6-hydroxy derivative 6c is not the 'active' metabolite since, like all other C- and N-hydroxylated benzothiazoles examined in this study, it is devoid of antitumor properties in vitro.

Aniline Compounds↗
PubMed1999

Molecular recognition between a new pentacyclic acridinium salt and DNA sequences investigated by optical spectroscopic techniques, proton nuclear magnetic resonance spectroscopy, and molecular modeling.

A pentacyclic acridine, 1H-2,3-dihydroindolizino[7,6,5-kl]acridinium chloride (1), related in structure to tetra- and pentacyclic marine natural products, has previously been shown to induce apoptosis in breast and non-small-cell lung tumor cell lines and shows significant differences in biological potency and antitumor profile from other intercalating agents based on the acridine framework. We report on the molecular recognition of the acridinium salt with DNA, quantified by optical spectroscopic methods, and have compared these results with the clinical agent amsacrine (m-AMSA). The results point to an intercalative association between 1 and G-C-rich sequences of DNA. We have synthesized a hexamer duplex d(ACGCGT)2, presenting two potential 5'-CpG recipient sites, and have investigated in detail by NMR and molecular modeling methods the orientational preferences of 1, particularly with regard to the pyrrolidine ring system. On the basis of the intermolecular nuclear Overhauser effect (NOE) data, four possible intercalation models were considered; no single model produced a significantly better fit than any of the others. The best fit to the experimental data was obtained by considering a dynamic equilibrium between the different intercalated orientations with the drug maximizing pi-overlap with the G-C base pairs at the intercalation site. We found little evidence for any degree of groove specificity imparted by the pyrrolidine ring. If these simulations have biological relevance they suggest that, at most, the agent induces only a transitory hot spot in the DNA which, evidently, is sufficient to be sensed by damage-recognition mechanisms of the cell.

Acridines↗
PubMed1999

Antitumor benzothiazoles. 7. Synthesis of 2-(4-acylaminophenyl)benzothiazoles and investigations into the role of acetylation in the antitumor activities of the parent amines.

2-(4-Aminophenyl)benzothiazoles display potent and selective antitumor activity against inter alia breast, ovarian, colon, and renal cell lines, but their mechanism of action, though yet to be defined, may be novel. Metabolism is suspected to play a central role in the mode of action of these benzothiazoles since drug uptake and biotransformation were observed in sensitive cell lines (e.g., breast MCF-7 and MDA 468 cells) in vitro, whereas insensitive cell lines (e.g., prostate PC 3 cells) showed negligible uptake and biotransformation. N-Acyl derivatives of the arylamines have been synthesized, and in vitro studies confirm N-acetylation and oxidation as the main metabolic transformations of 2-(4-aminophenyl)benzothiazoles, with the predominant process being dictated by the nature of the 3'-substituent. The prototype amine 3 underwent mainly N-acetylation in vitro, while 3'-substituted analogues 4 and 5 were primarily oxidized. N-Acetylation of 4 to 11 exerts a drastic dyschemotherapeutic effect in vitro, but acetylation of the halogeno congeners 5-7 gave acetylamines 12-14 which substantially retain selective antitumor activity. In vivo pharmacokinetic studies in rats confirmed rapid and exclusive N-acetylation of the 3'-methyl analogue 4, but less acetylation with the 3'-chloro analogue 5. Distinct expression patterns of N-acetyltransferase NAT1 and NAT2 have been demonstrated in our panel of cell lines.

Acetylation↗
PubMed1999

Antitumour imidazotetrazines. Part 37. Conjugation of the DNA major-groove alkylating imidazotetrazine mitozolomide to peptide motifs recognizing the minor groove.

Methods have been developed to conjugate the antitumour imidazotetrazines mitozolomide and temozolomide to DNA minor and major groove-binding peptidic motifs by solid phase peptide synthesis. Side chain deprotection and resin cleavage steps were accomplished under acidic conditions to maintain the structural integrity of the imidazotetrazine nucleus. When mitozolomide was conjugated to the DNA minor groove-binding peptide (SPKK)2-NH2 (3) a strong preference for binding with [dA-dT]2 sequences was observed by circular dichroism studies, consistent with the construct making non-covalent interactions within the minor groove. This conjugate showed a > 100-fold DNA alkylating activity compared with the free imidazotetrazine as measured by a Taq polymerase assay. Unexpectedly, alkylation patterns of all conjugates were nearly identical to those elicited by the major groove interactive agents cisplatin and the unconjugated imidazotetrazines temozolomide and mitozolomide, indicating that covalent modification was restricted to guanine sites in the major groove of DNA irrespective of the targeting property of the peptidic ligand. The electrophilic reactive chloroethyldiazonium ion intermediate formed in the breakdown of the imidazotetrazine ring of mitozolomide (methyldiazonium ion from temozolomide) must be liberated from the DNA-bound conjugate prior to the alkylation event, and must diffuse to and react with more nucleophilic sites in the major groove.

Amino Acid Sequence↗
PubMed1998

Inactivation of baroafferents leads to loss of barosensitivity without changes in nerve morphology.

Baroreceptors are stretch-sensitive mechanoreceptors, which are silenced by preventing distension of the receptor zone. Does chronic inactivation of these peripheral afferents alter their function or morphology? Compound action potentials and morphometry of carotid sinus nerves of 10 rabbits were investigated. The baroafferents were inactivated by embedding the pressure-released carotid sinus into silicon gel. The success of this procedure was validated by the absence of spike activity of the sinus nerve during normal and elevated systemic blood pressure. The contralateral vessels of the same animals were sham-operated and also embedded into silicon, but without prevention of wall movements. After 5, 7, 14 or 28 days the nerves were functionally reinvestigated before and after release of the sinus wall. Afterwards, the morphology of the nerve cross-sections was analysed by morphometry of electron micrographs. Baroafferents did not regain spike activity during immobilisation of the sinus wall. After release of the carotid sinus wall only nerves inactivated for five days regained their pulse synchronous baroreceptor discharge. Following seven days of inactivation, baroreceptor discharge could be elicited by maximal pressure elevation in only one of three nerves. At any time later, the baroreceptor response to arterial pressure changes was lost completely. The activity of the control nerves was preserved after 28 days. No obvious differences in fibre size and myelin thickness were observed between inactivated and control nerves. Inactivation of baroafferents for more than one week leads to a loss of pressure-dependent spike activity. Since morphology did not differ between inactivated and control nerves, it is suggested that changes of baroreceptor endings are responsible for this loss of function.

Action Potentials↗
PubMed1998

2-(4-Aminophenyl)benzothiazoles: novel agents with selective profiles of in vitro anti-tumour activity.

2-(4-Aminophenyl)benzothiazole (CJM 126) elicits biphasic growth-inhibitory effects against a panel of oestrogen receptor-positive (ER+) and oestrogen receptor-negative (ER-) human mammary carcinoma cell lines in vitro, yielding IC50 values in the nM range. Substitutions adjacent to the amino group in the 2-phenyl ring with a halogen atom or methyl group enhance potency in sensitive breast lines (pM IC50 values). Transient biphasic dose responses were induced but rapidly eradicated after specific drug exposure periods. Two human prostate carcinoma cell lines were refractory to the growth-inhibitory properties of 2-(4-aminophenyl)benzothiazoles; IC50 values > 30 microM were obtained. Potency and selectivity were confirmed when compounds were examined in the National Cancer Institute's Developmental Therapeutics screen; the spectrum of activity included specific ovarian, renal, colon as well as breast carcinoma cell lines. Moreover, comparing 6-day and 48-h incubations, the exposure time-dependent nature of the biphasic response was corroborated. Differential perturbation of cell cycle distribution followed treatment of MCF-7 and MDA 468 cells with substituted 2-(4-aminophenyl)benzothiazoles. In MDA 468 populations only, accumulation of events in G2/M phase was observed. Two MCF-7 cell lines were established with acquired resistance to CJM 126 (IC50 values > 20 microM), which exhibit cross-resistance to substituted benzothiazoles, but equal sensitivity to tamoxifen and doxorubicin. Compared with standard anti-tumour agents evaluated in the National Cancer Institute in vitro cell panel, benzothiazoles revealed unique profiles of growth inhibition, suggesting a mode(s) of action shared with no known clinically active class of chemotherapeutic agents.

Antineoplastic Agents↗
PubMed1998

Influence of 2-(4-aminophenyl)benzothiazoles on growth of human ovarian carcinoma cells in vitro and in vivo.

2-(4-Aminophenyl)benzothiazole molecules substituted in the 3 position of the phenyl ring with a halogen atom or methyl moiety comprise a group of compounds that potently inhibit specific human ovarian carcinoma cell lines. GI50 values fall within the nM range. Inhibition is highly selective -- whereas the GI50 value in IGROV1 cells consistently lies at < 10 nM, SK-OV-3 presents GI50 values > 10 microM. Biphasic dose-response relationships were observed in sensitive cell lines after 48-h drug exposure. COMPARE analyses revealed the very similar profiles of anti-tumour activity of 3-substituted benzothiazoles and 5-(4-dimethylaminophenylazo)quinoline, with Pearson correlation coefficients > 0.65. Anti-tumour activity extended to preliminary in vivo tests. The growth of OVCAR-3 cells in polyvinylidene fluoride (PVDF) hollow fibres implanted in the peritoneal cavity of mice was inhibited by more than 50% after intraperitoneal (i.p.) administration of 2-(4-amino-3-methylphenyl)benzothiazole (10 mg kg(-1)), 2-(4-amino-3-chlorophenyl)benzothiazole (100 mg kg(-1)) or 2-(4-amino-3-bromophenyl)benzothiazole (150 mg kg(-1)). The growth of OVCAR-3 tumours in subcutaneously (s.c.) implanted hollow fibres was retarded by more than 50% after treatment with 2-(4-amino-3-methylphenyl)benzothiazole (6.7 and 10 mg kg(-1)). In addition, the growth of s.c. OVCAR-3 xenografts was delayed after exposure to DF 203. However, the relationship between drug concentration and growth inhibition was inverse.

Animals↗
PubMed1998

Antitumour polycyclic acridines. Part 2. Physicochemical studies on the interactions between DNA and novel polycyclic acridine derivatives.

The noncovalent interactions between a series of new polycyclic acridine derivatives (1-5) and salmon testes DNA have been studied using several physicochemical techniques. These include spectrophotometric analysis, fluorescence quenching, thermal denaturation, and circular and linear dichroism. In order to compare the extent of the DNA binding by compounds 1-5 in their neutral and cationic forms, all experiments have been conducted at pH 7.4 and at pH 5.0. Other polynucleotides, including [Poly(dA-dT)]2 and [Poly(dG-dC)]2, were used in order to study the DNA base-pair binding specificity of these novel annelated acridine derivatives. The results indicate that the new polycyclic acridines display the following properties: (i) they are strong DNA-binding ligands with affinities 10- to 400-fold greater than that of acridine, 3- to 100-fold greater than that of m-AMSA (6) and 1- to 23-fold greater than that of proflavine at physiological pH (7.4); (ii) they have stronger DNA-binding activity at pH 5.0 as a result of the N-protonation of the aromatic chromophore; (iii) they bind more selectively to [Poly(dA-dT)]2 polynucleotide than to [Poly(dG-dC)]2 polynucleotide; (iv) within the series compound 3 binds to DNA less than compounds 1, 2, 4 and 5 at both pH values studied; and (v) the polycyclic acridines form a molecular complex with DNA undergoing intercalation inside the duplex macromolecule, as shown by linear and circular dichroism. Nevertheless, circular dichroism studies reveal alternative binding modes at low DNA: drug ratios.

Acridines↗
PubMed1998

Antitumour polycyclic acridines. Part 4. Physico-chemical studies on the interactions between DNA and novel tetracyclic acridine derivatives.

The non-covalent interactions between a series of new tetracyclic acridine derivatives (5-11) and DNA have been studied by spectrophotometric analysis, fluorescences quenching, thermal denaturation, and circular and linear dichroism. In order to compare the extent of the DNA binding by compounds 5-11 in their neutral and cationic forms, all experiments were conducted at pH 7.4 (physiological pH) and 5.0. The results indicated that compounds 5-11 are strong DNA-binding ligands with DNA affinities comparable to that of m-AMSA (1) or even higher. They showed a stronger DNA binding activity at pH 5.0 as a result of the N-protonation of the pyridoacridine aromatic chromophore. Ethidium-DNA fluorescence assays showed an A-T base pair preference of the binding distinguishing these novel compounds from simple acridines which show a slight G-C base pair preference. Circular and linear dichroism studies indicated that the drugs bind to DNA by undergoing intercalation inside the duplex macromolecule at high DNA:drug ratios and revealed alternative binding modes at low DNA:drug ratios.

Acridines↗
PubMed1997

Structural studies on bioactive compounds. 28. Selective activity of triazenyl-substituted pyrimethamine derivatives against Pneumocystis carinii dihydrofolate reductase.

Triazenyl-substituted pyrimethamine derivatives 10a-s have been prepared by coupling diazotized 2,4-diamino-5-(3-amino-4-chlorophenyl)-6-ethyl pyrimidine (1c) with a series of secondary amines in aqueous sodium carbonate solution. The triazenes which are stable and poorly soluble as free bases form more soluble, but unstable, salts with alkanesulfonic acids. The lead dimethyltriazene 2,4-diamino-5[4-chloro-3-(3,3-dimethyltriazen-1-yl)phenyl]-6-et hylpyrimidine (4a) forms a crystalline ethanesulfonic acid salt (solvated with 2-propanol), which is protonated at the pyrimidine N-1 position, as determined by X-ray crystallography. The ability of these new triazenes to inhibit Pneumocystis carinii dihydrofolate reductase in vitro has been compared to that of triazene 4a. The most potent and selective compound, 2,4-diamino-5-[3-[3-[2-(acetyloxy)ethyl]-3-benzyltriazen-1-y l]-4- chlorophenyl]-6-ethylpyrimidine (14a), has an IC50 value of 0.17 microM against the microbial enzyme and potentially useful selectivity (rat liver IC50/P. carinii IC50 = 114).

Animals↗
PubMed1996

Antitumor benzothiazoles. 3. Synthesis of 2-(4-aminophenyl)benzothiazoles and evaluation of their activities against breast cancer cell lines in vitro and in vivo.

A new series of 2-(4-aminophenyl)benzothiazoles substituted in the phenyl ring and benzothiazole moiety has been synthesized by simple, high-yielding routes. The parent molecule 5a shows potent inhibitory activity in vitro in the nanomolar range against a panel of human breast cancer cell lines, but is inactive (IC50 > 30 microM) against other cell types: activity against the sensitive breast lines MCF-7 and MDA 468 is characterized by a biphasic dose-response relationship. Structure-activity relationships derived using these cell types has revealed that activity follows the heterocyclic sequence benzothiazole > benzoxazole >> benzimidazole and that 2-(4-aminophenyl)benzothiazoles bearing a 3'-methyl- 9a, 3'-bromo- 9c, 3'-iodo- 9f, and 3'-chloro-substituent 9i are especially potent and their activity extends to ovarian, lung, and renal cell lines. Four compounds have been evaluated in vivo against human mammary carcinoma models in nude mice. Compound 9a showed the most potent growth inhibition against the ER+ (MCF-7 and BO) and ER- (MT-1 and MT-3) tumors. Our efforts to identify a pharmacological mechanism of action for these intriguing compounds have not, as yet, been successful.

Aniline Compounds↗
PubMed1996

[Conduction block in man is stimulation frequency dependent].

The action of local anaesthetics on isolated nerves is enhanced by high stimulation frequencies. The aim of our study was to investigate whether high-frequency stimulation enhances regional anaesthesia in man. METHODS. Seven healthy volunteers underwent three ulnar nerve blocks while non-noxious electrical stimulation with high (10, 50 Hz) or low (0.2 Hz) frequencies was applied via a widespread cutaneous electrode in the area supplied by the ulnar nerve. Perception was monitored continuously by means of a visual analogue scale. Skin temperature (infrared telethermometry) was evaluated every minute as an indicator of vasomotor block. After complete loss of perception or after 45 min, the spread of anaesthesia was determined by sharp-dull discrimination. The nerve block was preceded by a control stimulation of 45 min under otherwise identical conditions. RESULTS. During stimulation with 10 and 50 Hz, perception was lost significantly earlier than with 0.2 Hz. The spread of sensory block at the end of the experiments was also enhanced by stimulation with high frequencies, whereas the onset of vasomotor block (rise in skin temperature) remained unaltered. CONCLUSION. Non-oxious electrical stimulation with high frequencies significantly accelerates the onset of anaesthesia and extends the spread of sensory block.

Adult↗
PubMed1996

Effect of transcutaneous electrical nerve stimulation on onset of axillary plexus block.

We examined the effect of high frequency transcutaneous electrical nerve stimulation on the onset of brachial plexus block. Three groups of patients scheduled for surgery of the hand had a local anaesthetic block performed with 40 ml mepivacaine 1.5% using the axillary approach. After injection of the local anaesthetic transcutaneous electrical nerve stimulation was applied for 15 min either to the median nerve or the ulnar nerve; no stimulation was applied in the control group. Before and for 45 min after, the injection of local anaesthetic touch perception, pin prick, motor strength and skin temperature were tested by a blinded investigator in the areas supplied by the median, musculocutaneous, radial and ulnar nerves. There were no differences in the onset of block between the groups. Thus, the frequency-dependent action of local anaesthetics could not be demonstrated.

Adult↗
PubMed1995

Antitumor imidazotetrazines. 32. Synthesis of novel imidazotetrazinones and related bicyclic heterocycles to probe the mode of action of the antitumor drug temozolomide.

A series of new imidazo[5,1-d]-1,2,3,5-tetrazinones with additional hydrogen-bonding or ionic substituents at the 8-carboxamide position of the antitumor drugs temozolomide (1) and mitozolomide (2) has been prepared. None of these compounds were significantly more cytotoxic in vitro against the mouse TLX5 lymphoma than the lead structures. Molecular modeling techniques have been used to design benzo- and pyrazolo[4,3-d]-1,2,3-triazinones bearing carboxamide groups in appropriate positions which are isosteric with temozolomide and mitozolamide but which cannot ring open to alkylating species. As predicted, these compounds have no inhibitory properties against human GM892A or Raji cell lines in vitro. Temozolomide and the spermidine-temozolomide conjugate 28 preferentially methylate guanines within guanine-rich sequences in DNA, but no experimental evidence has been found to support the hypothesis that such regions are involved in catalyzing the ring opening of the imidazotetrazinone prodrugs to their active forms.

Animals↗
PubMed1995

Cancer Research Campaign phase II trial of temozolomide in metastatic melanoma.

PURPOSE: Sixty patients with metastatic melanoma were treated in a phase II study with the imidazotetrazine derivative temozolamide to assess further the efficacy demonstrated in previous phase I studies. PATIENTS AND METHODS: Fifty-five of 56 eligible patients were assessable for toxicity and 49 for response. The patients received temozolomide 150 mg/m2/d over 5 successive days orally (total dose, 750 mg/m2) in the first course. Courses were repeated every 4 weeks and the dose was escalated to 200 mg/m2/d x 5 (total dose, 1 g/m2) after the first course if toxicity was acceptable. Patients were all chemotherapy-naive, except for two who had previously received interferon alfa and one who had received interleukin-2 (the latter patient had also received two phase I drugs some time previously). RESULTS: A complete response (CR) was documented in three patients (all with lung metastases) and a partial response (PR) in nine patients (21% CR plus PR rate). Seven of 56 patients were not assessable for response because of early death or deterioration. The overall response rate excluding these patients is 12 of 49 (24%). The median response duration was 6 months (range, 2.5 to 22+). Toxicity of the regimen, which was mainly hematopoietic, was low. The median survival duration for all patients was 5.5 months (range, 0.5 to 29.5). For responders, the median survival duration was 14.5 months (range, 3 to 28+), with four patients still alive. CONCLUSION: Temozolomide in the schedule used has as good activity in chemotherapy-naive metastatic melanoma as the other most active agents currently in use. Further studies of the drug on its own and in combination with other agents is recommended.

Adolescent↗
PubMed1995

Structural studies on bioactive compounds. Part 26. Hydrogen bonding in the crystal structure of the N-methylformamide solvate of the immunomodulatory agent 2-amino-5-bromo-6-phenylpyrimidin-4-one (bropirimine): implications for the design of novel anti-tumour strategies.

The immunomodulatory agent bropirimine crystallizes from N-methylformamide (NMF) as a triply hydrogen-bonded duplex in the manner of a Watson-Crick guanine:cytosine base pair. The stoichiometry of the solvate is bropirimine:NMF (2:1) and all NMF molecules are in the Z-rotomeric form. The intermolecular hydrogen bonding is disrupted when the solvate is dissolved in deuteriated dimethyl sulphoxide at 37 degrees C. Bropirimine and other molecules which possess the 2-aminopyrimidin-4-one fragment are potentially capable of recognizing guanine or cytosine residues in single-stranded RNA or DNA by Watson-Crick bonding or double-stranded DNA by Hoogsteen bonds. The immunomodulatory properties of these compounds might be triggered by these encounters.

Adjuvants, Immunologic↗
PubMed1995

Structural studies on bioactive compounds. Part 27. Chemistry of the immunomodulatory agent bropirimine.

The 2-amino-6-phenylpyrimidin-4(3H)-ones bropirimine (1) and the debrominated analogue (4) undergo electrophilic nitration and sulphonation in the meta-position of the 6-phenyl group in strongly acidic conditions. Subsequent electrophilic substitutions take place in the 5-position of the pyrimidine ring, if vacant. Rearrangement of the 2-nitramino-6-phenyl-pyrimidines (22) and (23) furnishes the 2-amino-6-(3-nitrophenyl)pyrimidines (9) and (18), respectively. Nucleophilic substitutions, in contrast, occur readily in the pyrimidine 2-, 4- and 6-positions. Debromination of bropirimine by hydrazine hydrate can be rationalized by invoking an initial attack by the nucleophile at the electron-deficient pyrimidine 6-position. The reactive 4-chloro group in 5-bromo-4-chloro-2-formylamino-6-phenylpyrimidine (25) can be displaced with a range of nucleophiles (azide ion, ethanol, hydrazine, and primary and secondary aliphatic amines), without loss of the bromo substituent.

Adjuvants, Immunologic↗