Biomedical subjects

W A Remers

Publications and source records attributed to W A Remers.

At least 37 records · Page 2Linked to original sources

PubMed1990

Characterization of a unique tomaymycin-d(CICGAATTCICG)2 adduct containing two drug molecules per duplex by NMR, fluorescence, and molecular modeling studies.

Tomaymycin is a member of the pyrrolo[1,4]benzodiazepine [P(1,4)B] antitumor antibiotic group. This antibiotic is proposed to react with the exocyclic 2-amino group (N2) of guanine to form a covalent adduct that lies snugly within the minor groove of DNA. While DNA-footprinting experiments using methidiumpropyl-EDTA have revealed the favored bonding sequences for tomaymycin and related drugs on DNA, the stereochemistry at the covalent bonding site (C-11) and orientation in the minor groove were not established by these experiments. In previous studies using a combined fluorescence, high-field NMR, and molecular modeling approach, we have shown that for tomaymycin there are two diastereomeric species (11R and 11S) on both calf thymus DNA and d(ATGCAT)2. Although we were able to infer the identity (stereochemistry at C-11 and orientation in the minor groove) of the two species on d(ATGCAT)2 by high-field NMR and fluorescence studies, in combination with molecular mechanics calculations, definitive experimental evidence was lacking. We have designed and synthesized a self-complementary 12-mer [d(CICGAATTCICG)2] based on the Dickerson dodecamer [d(CGCGAATTCGCG)2] that bonds identically two tomaymycin molecules, each having a defined orientation and stereochemistry. Thus the bis(tomaymycin)-12-mer adduct maintains the self-complementarity of the original duplex molecule. Two-dimensional proton J-correlated spectroscopy (COSY) of the bis(tomaymycin)-d(CICGAATTCICG)2 adduct (I = inosine) unequivocally shows that C-11 of tomaymycin covalently bonds through N2 of guanine with an 11S stereochemistry in the sequence 5'-CGA-3'.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotics, Antineoplastic↗

PubMed1990

Alkylation of DNA by C-10 of 2,7-diaminomitosene.

Mitomycin C and certain analogues alkylate DNA with their C-1 position and cross-link it by a second alkylation involving C-10. We now show that monoalkylation by C-10 (carbamate group) can occur for mitosene analogues that have no reactive C-1 functionality. Sodium dithionite reduction of 2,7-diaminomitosene or 2,7-diamino-1-hydroxymitosene in the presence of calf thymus DNA resulted in alkylation of the DNA to the extent of one molecule per 14 and 11 bases, respectively, although no covalent binding was observed on catalytic reduction. Reduction of each of these mitosenes by sodium dithionite in the presence of 2'-deoxyguanosine gave monoalkylation on the 2-amino group of this nucleotide. The 2,7-diaminomitosenes inhibited L-1210 leukemia cell colony formation in vitro at concentrations 3-4-fold greater (less potent) than mitomycin C. DNA single-strand breaks were also produced by each mitosene, but these lesions did not correlate with cytotoxicity and were less prominent than breaks produced by another monofunctional alkylating agent, methyl methanesulfonate. Mitosene-induced DNA strand breaks are probably due to excission-repair endonuclease activity and not from oxygen free radicals produced by redox cycling of the quinone moiety. There was no evidence of DNA-DNA cross-links by either 2,7-diaminomitosene.

Alkylation↗

PubMed1990

DNA binding by antitumor anthracene derivatives.

The relative DNA binding strengths of bisantrene and nine new analogues were measured by spectrophotometric titration and melt transition temperature (Tm) techniques. Data from the spectrophotometric titrations could not be fit by simple Scatchard plots. However, they were fit by a McGhee-von Hippel equation over part of the binding range. The entire range of data was fit by a smoothing cubic spline function. The first derivative of this function gave, for each compound, a curve whose intercept provided a measure of relative binding strength. The delta Tm values agreed qualitatively with the spectrophotometric titration results, although there was not a precise linear relationship. Determinations of macroscopic pKas revealed that most of the compounds were dications at pH 7.0, but a few were mixtures of monocations and dications. No correlation was found between these binding studies and antitumor potencies in a clonogenic assay, which suggests that factors other than DNA binding can determine cytotoxicity for some of the analogues.

Animals↗

PubMed1990

All atom molecular mechanics simulations on covalent complexes of anthramycin and neothramycin with deoxydecanucleotides.

We present molecular mechanics simulations on covalent complexes between d[(GC)5]2, d(G10).d(C10), d(GCGCGAGCGC).d(GCGCTCGCGC), d(GCGCGTGCGC).d(GCGCACGCGC), d(G5AG4).d(C4TC5), and d(G5TG4).d(C4AC5) on one hand and potent antitumor antibiotics anthramycin and neothramycin A on the other, using the all atom force field in the framework of the program AMBER(UCSF). The energy-refined models of both the sets of complexes show minimal distortions for the nucleotides, consistent with the results of 2D NMR studies on these complexes. The drugs have 3'-orientation in the minor groove, consistent with the previously reported investigations employing the united atom force field and with the experimental observations. Both anthramycin and neothramycin are calculated to bind preferentially to the puGpu sequences over pyGpy. This is in qualitative agreement with experimental studies for anthramycin, while for neothramycin A, this result is in apparent disagreement with experimental observations which have reported preferential binding of neothramycin A to poly(dG-dC).poly(dG-dC) over poly(dG).poly(dC). While the present study brings out the usefulness of the simple molecular mechanics approach (using an all atom force field) in rationalizing substantial experimental observations, it also emphasizes the need for further investigations on solvent and dynamics effects in understanding the sequence specificity of drug-DNA binding.

Anthramycin↗

PubMed1989

Preparation and antitumor activity of additional mitomycin A analogues.

On the basis of qualitative structure-activity relationships developed in the preceding article, a series of 32 new mitomycin A analogues were prepared and tested in antitumor screens. Seven of them gave greater prolongation of life (ILS) than mitomycin C in the mouse P388 leukemia assay. They included examples with 7-O substituents such as cyclic ethers and nitrogen heterocycles. A Hansch analysis was attempted with log P and MR as the independent variables, but no statistically significant correlation could be made. Seven compounds, chosen mainly for their good potency (MED), were tested in the subcutaneous B16 melanoma assay in mice and four of them showed greater ILS than mitomycin C.

Animals↗

PubMed1989

New 2-substituted indoloquinone mitomycin analogues.

Previously reported 2-(hydroxymethyl)indoloquinones, prepared as their acetates or carbamates, were less active than 2-methyl analogues in bacterial cultures and they had no activity in mice, despite functionality appropriate for DNA cross-linking. On the basis of the hypothesis that these compounds might have been too reactive chemically for selective alkylation of DNA, we prepared new analogues with substituents that could give variation in the reduction potential of the quinone ring, which might control their rate of bioactivation. The 5-methoxyindoloquinones were much more potent cytotoxics than mitomycin C against human tumor cell lines, but they were inactive against P388 leukemia in mice. Two 5-aziridinylindoloquinones were also more potent than mitomycin C against the cell lines and one of them was active in the P388 model upon in vivo assay. The corresponding 5-amino analogues were less potent than mitomycin C against both the cell lines and murine P388 leukemia. A 2-(1-hydroxyethyl)carbamate was prepared by a 20-step synthesis. It was about one-fourth as potent as mitomycin C against two cell lines.

Antineoplastic Agents↗

PubMed1988

Computer simulation of the binding of quinocarcin to DNA. Prediction of mode of action and absolute configuration.

Computer-based models were derived for the covalent and noncovalent binding of the antitumor antibiotic quinocarcin to a representative DNA segment, d(ATGCAT)2. They showed that a mode of action, involving opening of the oxazolidine ring to give an iminium ion, followed by initial noncovalent binding in the minor groove and subsequent alkylation of the 2-amino group of guanine, was rational and attended by favorable interaction energies in each step. The best model had the aryl ring of quinocarcin lying in the 3' direction from the covalent binding site and an R configuration at the carbon involved in covalent bond formation. It also showed that the preferred absolute configuration for quinocarcin was the reverse of that arbitrarily assigned in the literature.

Computer Simulation↗

PubMed1988

Nucleotide derivatives of 2,7-diaminomitosene.

Treatment of mitomycin C with pyrimidine nucleotides in acidic media produced derivatives of 2,7-diaminomitosene in which C-1 was covalently bound to the phosphate group of the nucleotides. On reduction, these derivatives liberated the nucleotides and a mitomycin intermediate that alkylated DNA. Their reduction in the presence of 2'-deoxyguanosine produced some bifunctional alkylation as did mitomycin C. They were readily taken up by L1210 leukemia cells, in which they showed potent cytotoxicity. These properties suggest that they are acting as prodrugs capable of conversion into two active species. The uridylate derivative showed activity comparable to that of mitomycin C against P-388 leukemia in mice.

Alkylation↗

PubMed1988

Conformations of complexes between mitomycins and decanucleotides. 3. Sequence specificity, binding at C-10, and mitomycin analogues.

Molecular mechanics simulation of the interactions of mitomycin C and certain analogues with DNA models are presented. The sequence specificity of mitomycin C binding was investigated by using a d(GCGCGCGCGC)2 decanucleotide duplex, abbreviated herein as GC10, in which the base pair was varied on either side of the covalent binding site. A CGT fragment was favored, although its correlation with the diverse findings in the literature is questionable. A model was derived for the monocovalent binding at C10 of 2,7-diaminomitosene with GC10 and for the noncovalently bound hydroquinone intermediate. Revised models were established for three highly active mitomycin C analogues: M-83, BMY-25282, and RR-150. They involved covalent binding at the 2-amino group of a guanine residue, and they accounted for enhanced noncovalent binding afforded by specific interactions of the C7 substituents with residues in GC10.

Animals↗

PubMed1987

Preparation and antitumor activity of new mitomycin A analogues.

A series of 26 mitomycin A analogues including 23 new ones was prepared by a variety of methods. The most useful methods were alkoxide exchange on mitomycin A and treatment of 7-hydroxymitosane with 3-substituted 1-phenyltriazenes. Many of the new analogues were superior to mitomycin C in the P388 leukemia assay and the more stringent subcutaneous B16 melanoma assay both in mice. Four of them gave long-term survivors in the latter assay. Quantitative correlations between log P and antitumor activity were not possible, but some guidelines for future analogue development are proposed.

Animals↗

PubMed1987

New antitumor agents containing the anthracene nucleus.

A series of 21 new compounds related to bisantrene was synthesized and tested in vitro by using clonogenic assays against a variety of human tumor cell lines, fresh human tumors, and P-388 leukemia. Those most closely related to bisantrene were less active than it was, but a subset of compounds with saturated side chains containing two basic nitrogens showed good activity. Two compounds of this subset, N,N'-bis[2-(dimethylamino)ethyl]-9,10-anthracenebis(methylamine)(6 ), and N,N'-bis(1-ethyl-3-piperidinyl)-9,10-anthracenebis(methylamine)(19 ), were very active in vitro against human tumor cell lines, but not active against fresh human tumors or P-388 leukemia cells. They had only marginal activity in mouse tumor models. Thus, the fresh human tumors and P-388 leukemia cells in vitro were better predictors than the established cell lines for the activity of these anthracene compounds in vivo against mouse tumors. These compounds appear to be distinct from bisantrene in aspects of mode of action. For example, 6 did not cause inhibition of macromolecular synthesis and promotion of DNA single strand breakage at cytotoxic drug concentrations. Toxicological studies showed that its rapid administration caused acute neurotoxicity resulting in apnea. It also produced skin ulcers on id administration, but they were less severe than those caused by bisantrene.

Animals↗

PubMed1986

Metal complexes of mitomycins.

The preparation of stable complexes between the N7-[2-(2-pyridyl)ethyl] and N7-(2-piperazinylethyl) derivatives of mitomycin C and metal ions such as Cu(II), Zn(II), and Pt(II) was accomplished. Mitomycin C did not form stable complexes, but it rearranged to a mitosene capable of complex formation. Some of these complexes had antitumor activity in mice. However, they were less active than mitomycin C. Weak associations between mitomycin C and metal ions were demonstrated by 13C and 15N NMR spectrometry.

Animals↗

PubMed1986

Aminoglycoside antibiotics. 6. Chemical reactions of aminoglycosides with disodium carbenicillin.

Aminoglycoside antibiotics including kanamycin A, tobramycin, and the gentamicin C complex reacted with 1 mol of disodium carbenicillin to give products derived from acylation of their amino groups by the beta-lactam function of the carbenicillin. Amikacin was acylated by two carbenicillin units. Chromatographic analysis of fragments from the acid hydrolysis of these derivatives showed that the preferred site of acylation was in the 2-deoxystreptamine unit of the aminoglycosides. The two sites of acylation in amikacin were the 6'-amino group and the amino group in the aminohydroxybutyryl substituent. The derivatives had almost no antibacterial activity, and they were not toxic.

Acylation↗

PubMed1986

Conformations of complexes between mitomycin and decanucleotides. 2. Application of the model to mitomycin C derivatives. Extension to covalent binding with adenine.

Molecular mechanics simulation of the interactions of important mitomycin C analogues monocovalently bound to DNA models are presented. These analogues included substituents such as p-hydroxyphenyl, 2-mercaptoethyl, and dimethylamidinium on N7 of mitomycin C and the DNA models consisted of d(GCGCGCGCGC)2 and d(GCGCATGCGC)2. The excellent fits and strong binding affinities of these highly potent analogues support the usefulness of the model. The binding of a mitomycin-related N-phenylpyrrole with a carbamoyloxy substituent to 06 of guanine was studied. Finally, a reactive mitomycin intermediate proposed by Moore was shown to interact with DNA in a way consistent with the formation of a covalent adduct.

Base Sequence↗

PubMed1986

Mitomycin C analogues with increased metal complexing ability.

Twenty-three new mitomycin C analogues designed to have increased metal complexing ability were synthesized and tested against P388 leukemia in mice. Their ability to complex Cu(II) was revealed by the shifts in their UV absorption spectra caused by this metal. One analogue was clearly more active than mitomycin C in the antitumor assay and two others had good activity. Correlation between antitumor activity and Cu(II) complexing ability was ambiguous. The most active compounds were either not complexers or they were complexers limited to the 2-(2-pyridyl)alkyl type substituent on N7. A variety of amino acid substituents on N7 showed only weak antitumor activity.

Animals↗

PubMed1986

Preparation and antitumor activity of 7-substituted 1,2-aziridinomitosenes.

7-Methoxy-1,2-aziridinomitosenes were prepared from mitomycin A and its N-methyl homologue by catalytic reduction followed by air oxidation. Treatment of these products with amines, including ammonia, ethylenimine, 2-methylethylenimine, propargylamine, and furfurylamine gave the corresponding 7-(substituted amino) derivatives. Screening of these compounds against P-388 leukemia in mice revealed some good activities. The more easily reduced compounds gave prolongation of life span comparable to that of mitomycin C, but their optimal doses were higher. Among these compounds, a methyl group on the aziridine nitrogen increased potency. The 7-amino derivatives, which were difficult to reduce to hydroquinones, were essentially inactive. The aziridinomitosenes were subjected to a Hansch-type analysis, but no statistically significant correlation was found.

Animals↗

PubMed1986

Conformations of complexes between pyrrolo[1,4]benzodiazepines and DNA segments.

The molecular mechanics program AMBER, assisted by CHEMLAB II, was used to model the covalent and noncovalent binding of anthramycin, tomaymycin, and neothramycin A to the hexanucleotide conformation. Structures covalently bonded at N2 of guanine gave excellent fits when placed in either direction in the minor groove. However, energy analysis showed a preference for the direction wherein the side chain points toward the 5' end of the covalently bound strand. This preference agrees with published NMR studies. Noncovalent binding of anthramycin in the minor groove near guanine gave good fits with almost no distortion in the helix, and the reactive center of the ligand was close enough to N2 for subsequent covalent bond formation. Anthramycin also gave a good noncovalent complex near adenine in the minor groove, but binding in the major groove had decreased dispersion attractions. Binding of tomaymycin was similar to that of anthramycin, although the smaller size of tomaymycin resulted in less binding energy. Neothramycin noncovalent binding was characterized by strong electrostatic interactions, partly involving the 3-OH group, and by part of the molecule lying outside the minor groove. AMBER was used for the exploratory design of an anthramycin analogue that theoretically would bind as well as anthramycin but not cause cardiotoxicity. A related study involving anthramycin, tomaymycin, and the pentanucleotide duplex d(AAGAA/TTCTT) was undertaken to evaluate further the ability of AMBER to predict sequence specificity. It indicated a preferred direction of binding toward 5' in the minor groove of the duplex, but rather weak interaction with the noncovalently bound strand. This prediction agreed with experiments on tomaymycin that showed separation of the duplex and alignment of the drug toward the 5' end of the covalently bound strand.

Anthramycin↗

PubMed1986

Aminoglycoside antibiotics. 7. Dihydrostreptomycin analogues.

Dihydrostreptomycin analogues with structural variations in their guanidino groups were prepared. The analogue with a methyl group on the guanidine at C-1 was nearly as active as dihydrostreptomycin against bacteria. However, the 2-imidazolin-2-ylamino substituent at C-1 eliminated activity. No analogue with a substituent on the C-3 guanidino group was active.

Dihydrostreptomycin Sulfate↗