Design and Synthesis of a Nitrogen Mustard Derivative Stabilized by Apo-neocarzinostatin

Neocarzinostatin (NCS) is an antitumor antibiotic comprising a 1:1 protein-chromophore complex and exhibits cytotoxic action through DNA cleavage via H-abstraction. Cytotoxic activity resides with the chromophore 1 alone, while the protein (apoNCS) protects and transports labile 1. The naphthoate portion (2) of NCS chromophore (1) is important for binding to apoNCS and DNA intercalation. In this paper we describe our attempts to use apoNCS to improve the hydrolytic stability of novel bifunctional DNA alkylating agents. The nitrogen mustards, melphalan and chlorambucil, were both conjugated to 2, and the biological activities of these conjugates were assessed. Chlorambucil did not benefit from conjugation. The melphalan conjugate (6) formed covalent DNA adducts at guanine bases and exhibited greater in vitro cytotoxic activity than unmodified melphalan. Fluorescence and NMR spectroscopy showed that 6 binds to apoNCS. Binding to apoNCS-protected 6 reduced the extent of hydrolysis of the conjugate. This novel approach demonstrates for the first time that an enediyne apo-protein can be used to improve the stability of substances that are of potential interest in cancer chemotherapy.

Anionic carbonato and oxalato cobalt(iii) nitrogen mustard complexesElectronic supplementary information (ESI) available: Table of hydrogen bonds for 6b and 8. See http://www.rsc.org/suppdata/dt/b3/b311091e/

Synthetic approaches to cobalt(III) complexes [Co(L)(L')2] containing the bidentate dialkylating nitrogen mustard N,N-bis(2-chloroethyl)-1,2-ethanediamine (L = dce) together with anionic ancilliary ligands (L') which are either carbonato (CO3(2-)), oxalato (ox2-), bis(2-hydroxyethyl)dithiocarbamato (bhedtc-), 2-pyridine carboxylato (pico-) or 2-pyrazine carboxylato (pyzc-) were investigated. Synthetic routes were developed using the related amines N,N-diethyl-1,2-ethanediamine (dee) and 1,2-ethanediamine (en). The complexes [Co(CO3)2(L)]- (L = dee 1, dce 2), [Co(ox)2(L)]- (L = dee 3, dce 4), [Co(bhedtc)2(dee)]+ 5, [Co(bhedtc)2(en)]+ 6, mer-[Co(pico)3], mer-[Co(pyzc)]3 7 and [Co(pico)2(dee)]+ 8 were prepared and were characterised by IR, UV-Vis, 1H and 13C[1H] NMR spectroscopy, mass spectrometry and cyclic voltammetry. [Co(bhedtc)2(en)]BPh4 6b and trans(O)-[Co(pico)2(dee)]ClO4 8 were characterised by X-ray crystallography. In vitro biological tests were carried out on complexes 1-4 in order to assess the degree to which coordination of the mustard to cobalt attenuated its cytotoxicity, and the differential toxicity in air vs. nitrogen.

Synthesis and Evaluation of Nitroheterocyclic Carbamate Prodrugs for Use with Nitroreductase-Mediated Gene-Directed Enzyme Prodrug Therapy

A variety of nitroheterocyclic carbamate prodrugs of phenylenediamine mustard and 5-amino-1-(chloromethyl)-3-[(5,6,7-trimethoxyindol-2-yl)carbonyl]-1,2-dihydro-3H-benz[e]indoline (amino-seco-CBI-TMI), covering a wide range of reduction potential, were prepared and evaluated for use in gene-directed enzyme prodrug therapy (GDEPT) using a two-electron nitroreductase (NTR) from Escherichia coli B. The carbamate prodrugs and corresponding amine effectors were tested in a cell line panel comprising parental and NTR-transfected human (SKOV3/SKOV3-NTR(neo), WiDr/WiDr-NTR(neo)), Chinese hamster (V79(puro)/V79-NTR(puro)), and murine (EMT6/EMT6-NTR(puro)) cell line pairs and were compared with the established NTR substrates CB1954 (an aziridinyl dinitrobenzamide) and the analogous dibromomustard. The 1-methyl-2-nitroimidazol-5-ylmethyl carbamate of phenylenediamine mustard was metabolized rapidly by EMT6-NTR(neo) but not EMT6 cells, demonstrating that it is an efficient substrates for NTR. Despite this, the carbamates of phenylenediamine mustards show relatively low differential cytotoxicity for NTR+ve cells in IC(50) assays, apparently because they retain sufficient alkylating reactivity that most of the prodrug reacts with nucleophiles during the drug exposure period. In contrast, the corresponding amino-seco-CBI-TMI prodrugs were less efficient NTR substrates but had greater chemical stability, were more potent, and showed substantial NTR-ve/NTR+ve ratios in the cell line panel, with ratios of 15-100-fold for the 1-methyl-2-nitro-1H-imidazol-5-ylmethyl and 1-methyl-5-nitro-1H-imidazol-2-ylmethyl carbamates of amino-seco-CBI-TMI. The activity of these two prodrugs was evaluated against NTR-expressing EMT6 tumors comprising ca. 10% NTR+ve cells. Small but not statistically significant killing of NTR+ve cells was observed, with no effect against NTR-ve target cells. The lack of activity against NTR+ve cells in tumors, despite potent and selective activity in culture, indicates that pharmacokinetic optimization will be required if in vivo efficacy against solid tumors is to be achieved with this new class of NTR prodrugs.

Synthesis of aromatic nitrogen mustard agents and analysis of their alkylation activity at physiological pH and temperature

A Structure Activity Relationship (SAR) study was accomplished with six aromatic compounds which have a nitrogen mustard (N-mustard) substituent. N-mustard agents are very important for the clinical treatment of many types of cancers. All N-mustard agents synthesized alkylated a nucleophilic primary amine (p-chloroaniline) in aqueous solvent at pH 7.4 and 37 degrees C. Rate constants and rate equations were determined for the alkylation reactions by monitoring the formation of a fluorescent complex formed when fluorescamine complexes the unreacted p-chloroaniline. Fluorescamine complexation of the unreacted primary amine halts the alkylation reaction and allows the determination of remaining unreacted primary amine, which in turn permits the determination of rate constants and rate equations. The fluorescamine-amine complex shows a strong absorbance peak at a wavelength of 400 nanometers in aqueous solvent. The molar absorptivity (epsilon) was calculated to be 18.37 L/(mole x cm). First order rate constants ranged from 0.513E-2 minute(-1) to 1.32E-2 minute(-1) with second order rate constants from 2.85E-2 (M x minute)(-1) to 4.78E-2 (M x minute)(-1). The aromatic compounds included benzoic acid, m-chlorobenzoic acid, hydrocinnamic acid, m-toluic acid, and 3,4-dimethoxybenzoic acid. The synthesis procedure produced the N-mustard agents at > or = 90% yield and high purity. Partition coefficient Log(Kow)Log P values ranged from 2.66 to 4.18. The N-mustard agents consisted of greyish-yellow crystals which retained alkylation activity for more than ten weeks when stored at -10 degrees C and were soluble in water at 25 degrees C and 37 degrees C.

Bifunctional constructs of aspirin and ibuprofen (non-steroidal anti-inflammatory drugs; NSAIDs) that express antibacterial and alkylation activities

Ibuprofen and aspirin are two common non-steroidal anti-inflammatory drugs (NSAIDs). Both NSAIDs have a carbonyl carbon [-C(O)-], which was utilized to attach a nitrogen mustard (N-mustard) ester group or a tripeptide group. The tripeptide consisted of a L-Gly-D-Ala-D-Ala sequence, where D-Ala-D-Ala is the reactive site for antibacterial activity and L-Gly serves as a linker to the NSAID carrier drug. The aspirin tripeptide and N-mustard show significant antibacterial activity at >or=5.0 x 10(-5) M against penicillin-susceptible or -resistant Escherichia coli. The partition coefficients (log Kow)log P of aspirin and ibuprofen tripeptide drugs were -1.05 and 2.23, respectively. The NSAIDs served as carrier drugs of the N-mustard group which expressed alkylation activity directed towards the nucleophilic primary amine of p -chloroaniline. Hydrolysis of the N-mustard agents yielded the parent structure of aspirin (or ibuprofen) and an N-mustard moiety, 2-[bis(2-chloroethyl)amino]ethanol. The (log Kow)log P for the N-mustard structures of aspirin and ibuprofen were 2.61 and 5.63, respectively. The (log Kow)log P value of 2-[bis(2-chloroethyl)amino]ethanol was 0.56. Fluorescamine was utilized to determine unreacted p -chloroaniline at known time intervals, which permitted calculation of rate constants and rate equations. The aspirin N-mustard agent expressed strong antibacterial activity against a penicillin-resistant bacteria and first-order alkylation kinetics. The ibuprofen N-mustard and 2-[bis(2-chloroethyl)amino]ethanol followed second-order alkylation kinetics. All N-mustard and tripeptide compounds showed zero violations of the Rule of 5. Values of TPSA (molecular polar surface area), C log P and molecular dipoles were calculated.

Enhanced hydrolytic stability and water solubility of an aromatic nitrogen mustard by conjugation with molecular umbrellas

Chlorambucil, an aromatic nitrogen mustard, has been conjugated to putrescine- and spermidine-based scaffolds bearing one, two, and four persulfated cholic acid units. Those conjugates bearing two or four sterols show improved hydrolytic stability and water solubility relative to chlorambucil. A similar conjugate that contained only one sterol unit shows negligible improvement in hydrolytic stability but a significant increase in water solubility. Qualitatively, the hydrolytic stability within this series of conjugates parallels the shielding effects that have previously been found for related conjugates bearing a pendant, hydrophobic fluorescent probe. In vitro studies indicate that these conjugates possess modest to moderate activity against certain human lymphoblastic leukemia and human colon carcinoma cells.

New carbocyclic lexitropsins with dinitromustard as N-terminal fragment. Inhibition of topoisomerases

A series of carbocyclic lexitropsins was evaluated for their capacity to inhibit human topoisomerases I and II. The synthesized compounds were carbocyclic oligopeptides with dinitromustard as N-terminal fragment. In the topoisomerases I and II assays, the relaxation of DNA were inhibited with all four compounds. This inhibition was directly proportional to the compound concentration.

A new approach for evaluating in vivo anti-leukemic activity using the SCE assay. An application on three newly synthesised anti-tumour steroidal esters

Three newly synthesised steroidal esteric derivatives of nitrogen mustard (compounds 1-3) were comparatively studied on a molar basis regarding their ability to induce sister chromatid exchanges (SCEs) in normal human lymphocytes in vitro and therapeutic effects on leukemia P388 bearing mice. Compounds 1 and 3 are modified steroidal esters of p-methyl-m-N,N-bis(2-chloroethyl)amino benzoic acid, and compound 2 is a modified steroidal ester of chlorambucil. All compounds induced statistically significant increases in SCEs and decreases in proliferation rate indices (PRIs) of cultured human lymphocytes and significantly increased the life span of P388 bearing mice. In this study, the doses applied for therapeutic purposes upon leukemia P388 bearing mice in vivo were derived from cytogenetic observations in normal human lymphocytes in vitro. A substantially better therapeutic effect was obtained compared to the effect achieved after the use of quite higher doses related with LD(10) values. We have demonstrated that the order of anti-tumour effectiveness of the treatment schedules of the three newly synthesised compounds tested (at doses derived from cytogenetic observations) coincides with the order of the cytogenetic effects they induce. The SCE assay appears to have an application in the clinical prediction of tumour sensitivity to potential chemotherapeutics.

Antitumor imidazotetrazines. 41. Conjugation of the antitumor agents mitozolomide and temozolomide to peptides and lexitropsins bearing DNA major and minor groove-binding structural motifs

Carboxylic acids derived from the amido groups of the antitumor agents mitozolomide and temozolomide have been conjugated to simple amino acids and peptides by carbodiimide coupling. Solid-state peptide synthesis has been applied to link the acids to DNA major groove-binding peptidic motifs known to adopt alpha-helical conformations. Attachment of the acids to pyrrole and imidazole polyamidic lexitropsins gave a series of potential DNA minor groove-binding ligands. In vitro biological evaluation of a limited number of these novel conjugates failed to demonstrate any enhanced growth-inhibitory activity compared to the unconjugated drugs; sites of alkylation at tracts of multiple guanines were also unaffected. Attachment of additional residues at C-8 of the imidazotetrazines did not perturb the chemistry of activation of the bicyclic nucleus, and biological sequelae can be rationalized by invoking the liberation of a common, diffusible, reactive chemical intermediate, the methanediazonium ion.

Metabolism and mechanisms of action of bendamustine: rationales for combination therapies

Bendamustine hydrochloride is the active ingredient of Ribomustin (Ribosepharm GmbH, Munich, Germany). It was first synthesized in 1963 in the German Democratic Republic. Bendamustine is chemically related to the alkylating agent chlorambucil, with the benzene ring in the chlorambucil molecule replaced by a 1-methyl-benzimidazole moiety. The mechanisms of action of bendamustine have been under investigation since the early 1960s, and its first use was as a treatment for multiple myeloma in 1969. Bendamustine has three active moieties: an alkylating group, in common with the nitrogen mustard family; a benzimidazole ring, which may act as a purine analog; and a butyric acid side-chain. Bendamustine undergoes extensive first-pass metabolism. However, unmetabolized bendamustine accounts for about 45% of the total drug recovered in urine. The main transformation product is a cytotoxic hydroxy metabolite (beta-hydroxybendamustine). Bendamustine was originally synthesized with the intention of producing an antineoplastic agent with low toxicity and both alkylating and antimetabolic properties. However, it has been shown that, at least at high concentrations, it acts primarily as an alkylating agent. Based on the multiple actions and cell cycle effects of this agent, mechanism-based combination strategies have been suggested. The rationales behind bendamustine combination regimens and the importance of the sequence of administration of different drugs are explored.

Targeting critical regions in genomic DNA with AT-specific anticancer drugs

Cellular DNA is not a uniform target for DNA-reactive drugs. At the nucleotide level, drugs recognize and bind short motifs of a few base pairs. The location of drug adducts at the genomic level depends on how these short motifs are distributed in larger domains. This aspect, referred to as region specificity, may be critical for the biological outcome of drug action. Recent studies demonstrated that certain minor groove binding (MGB) drugs, such as bizelesin, produce region-specific lesions in cellular DNA. Bizelesin binds mainly T(A/T)(4)A sites, which are on average scarce, but occasionally cluster in distinct minisatellite regions (200-1000 bp of approximately 85-100% AT), herein referred to as AT islands. Bizelesin-targeted AT islands are likely to function as strong matrix attachment regions (MARs), domains that organize DNA loops on the nuclear matrix. Distortion of MAR-like AT islands may be a basis for the observed inhibition of new replicon initiation and the extreme lethality of bizelesin adducts (<10 adducts/cell for cell growth inhibition). Hence, long AT-islands represent a novel class of critical targets for anticancer drugs. The AT island paradigm illustrates the potential of the concept of regional targeting as an essential component of the rational design of new sequence-specific DNA-reactive drugs.

Benzoyl and cinnamoyl nitrogen mustard derivatives of benzoheterocyclic analogues of the tallimustine: synthesis and antitumour activity

A series of benzoyl and cinnamoyl nitrogen mustards tethered to different benzoheterocycles and to oligopyrroles structurally related to netropsin consisting of two pyrrole-amide units and terminating with an amidine moiety have been synthesised and a structure--activity relationship determined. Derivatives 3--10 have been evaluated for their sequence selective alkylating properties and cytotoxicity against human K562 leukaemia cells. They are 2- to 50-fold less cytotoxic than tallimustine, with compound 8 being the most potent member of this series. Among tallimustine isosters, the compounds with an indole 3 or benzothiophene 6 are 4-fold less cytotoxic than tallimustine, while the compounds with an N-methyl indole or benzofuran showed a 7- and 14-fold reduced cytotoxic potency, respectively. Our preliminary results indicate that these derivatives preferentially bind to AT-rich sequence with a sequence selectivity similar to tallimustine.

Synthesis and antibacterial activity of dual-action agents of a beta-lactam antibiotic with cytotoxic agent mitozolomide or temozolomide

Dual-action agents 5a-f and 12a-f, a beta-lactam antibiotic combined with a cytotoxic agent, mitozolomide (Meto) or temozolomide (Temo), were synthesised. The antibacterial activity (MICs) of the dual-action agents has been determined against a panel of bacteria including several beta-lactamase producing strains. The tests showed 5a-f active against the non-beta-lactamase producing methicillin sensitive Staphylococcus aureus (MSSA) strains, however, little synergistic effect between the beta-lactam and the cytotoxic agent was observed. 12a-f demonstrated some synergistic effect against bacteria. 12a, in particular, is active against ampicillin resistant (beta-lactamase-producing) strains of Serratia marcescens.

A comparative study on cytogenetic and antineoplastic effects induced by two modified steroidal alkylating agents

We investigated the effects of two newly synthesized steroidal derivatives of nitrogen mustard on sister chromatid exchange rates and on human lymphocyte proliferation kinetics. The compound 33-hydroxy-5alpha,22alpha-spirostan- 12-one-p-(N,N-bis(2-chloroethyl)amino)phenylacetate(1) was, on a molar basis, less effective in inducing sister chromatid exchange and suppressing cell proliferation rate indices than compound 3beta-hydroxy-12alpha-aza-C-homo-5alpha,22alpha-spirostan-12-one-p-(N,N-bis(2-chloroethyl)amino)phenylacetate(2). A correlation was observed between the magnitude of the sister chromatid exchange response and the depression of cell proliferation index. We also studied the effects of the aforementioned compounds on Lewis lung carcinoma. The order of the percent inhibition of tumor growth achieved by the compounds coincides with the order of the cytogenetic effects they induce.

Hypoxia-selective antitumor agents. 16. Nitroarylmethyl quaternary salts as bioreductive prodrugs of the alkylating agent mechlorethamine

Nitrobenzyl quaternary salts of nitrogen mustards have been previously reported as hypoxia-selective cytotoxins. In this paper we describe the synthesis and evaluation of a series of heterocyclic analogues, including pyrrole, imidazole, thiophene, and pyrazole examples, chosen to cover a range of one-electron reduction potentials (from -277 to -511 mV) and substitution patterns. All quaternary salt compounds were less toxic in vitro than mechlorethamine, and all were more toxic under hypoxic than aerobic conditions, although the differentials were highly variable within the series. The most promising analogue, imidazole 2, demonstrated DNA cross-linking selectively in hypoxic RIF-1 cells, and was active in vivo in combination with radiation or cisplatin. However, 2 also produced unpredictable toxicity in vivo, suggestive of nonspecific nitrogen mustard release, and this has restricted further development of these compounds as hypoxia-selective cytotoxins.

Melanocyte-Directed enzyme prodrug therapy (MDEPT): development of second generation prodrugs for targeted treatment of malignant melanoma

Evaluation of second generation prodrugs for MDEPT, by oximetry, has highlighted structural properties that are advantageous and disadvantageous for efficient oxidation using mushroom tyrosinase. In particular, a sterically undemanding prodrug bis-(2-chloroethyl)amino-4-hydroxyphenylaminomethanone 28 was synthesised and found to be oxidised by mushroom tyrosinase at a superior rate to tyrosine methyl ester, the carboxylic acid of which is the natural substrate for tyrosinase. The more sterically demanding phenyl mustard prodrugs 9 and 10 were oxidised by mushroom tyrosinase at a similar rate to tyrosine methyl ester. In contrast, tyramine chain elongation via heteroatom insertion was detrimental and the rate of mushroom tyrosinase oxidation of phenyl mustard prodrugs 21 and 22 decreased by 10 nanomol/min.

Accumulation of gamma-globin mRNA and induction of erythroid differentiation after treatment of human leukaemic K562 cells with tallimustine

Human leukaemic K562 cells can be induced in vitro to erythroid differentiation by a variety of chemical compounds, including haemin, butyric acid, 5-azacytidine, cytosine arabinoside, mithramycin and chromomycin, cisplatin and cisplatin analogues. Differentiation of K562 cells is associated with an increase of expression of embryo-fetal globin genes, such as the zeta-, epsilon- and gamma-globin genes. The K562 cell line has been proposed as a very useful in vitro model system to determine the therapeutic potential of new differentiating compounds as well as to study the molecular mechanism(s) regulating changes in the expression of embryonic and fetal human globin genes. Inducers of erythroid differentiation stimulating gamma-globin synthesis could be considered for possible use in the therapy of haematological diseases associated with a failure in the expression of normal beta-globin genes. We have analysed the effects of tallimustine and distamycin on cell growth and differentiation of K562 cells. The results demonstrated that tallimustine is a potent inducer, while distamycin is a weak inducer, of K562 cell erythroid differentiation. Erythroid differentiation was associated with an increase of accumulation of gamma-globin mRNA and of production of both haemoglobin (Hb) Gower 1 and Hb Portland. In addition, tallimustine-mediated erythroid induction occurred in the presence of activation of the apoptotic pathway. The reasons for proposing tallimustine as an inducer of gamma-globin gene expression are strongly sustained by the finding that this compound stimulates fetal haemoglobin production in human erythroid precursor cells from normal subjects.

DNA minor groove alkylating agents

Recent work on a number of different classes of anticancer agents that alkylate DNA in the minor groove is reviewed. There has been much work with nitrogen mustards, where attachment of the mustard unit to carrier molecules can change the normal patterns of both regio- and sequence-selectivity, from reaction primarily at most guanine N7 sites in the major groove to a few adenine N3 sites at the 3'-end of poly(A/T) sequences in the minor groove. Carrier molecules discussed for mustards are intercalators, polypyrroles, polyimidazoles, bis(benzimidazoles), polybenzamides and anilinoquinolinium salts. In contrast, similar targeting of pyrrolizidine alkylators by a variety of carriers has little effect of their patterns of alkylation (at the 2-amino group of guanine). Recent work on the pyrrolobenzodiazepine and cyclopropaindolone classes of natural product minor groove binders is also reviewed.

Identification of the nitrogen-based blister agents bis(2-chloroethyl)methylamine (HN-2) and tris(2-chloroethyl)amine (HN-3) and their hydrolysis products on soil using ion trap secondary ion mass spectrometry

The nitrogen blister agents HN-2 (bis(2-chloroethyl)methylamine) and HN-3 (tris(2-chloroethyl)amine) were directly analyzed on the surface of soil samples using ion trap secondary ion mass spectrometry (SIMS). In the presence of water, HN-1 (bis(2-choroethyl)ethylamine), HN-2 and HN-3 undergo hydrolysis to form N-ethyldiethanolamine, N-methyldiethanolamine and triethanolamine (TEA), respectively; these compounds can be readily detected as adsorbed species on soil particles. When soil samples spiked with HN-3 in alcohol were analyzed, 2-alkoxyethylamine derivatives were observed on the sample surfaces. This result shows that nitrogen blister agents will undergo condensation reactions with nucleophilic compounds and emphasizes the need for an analytical methodology capable of detecting a range of degradation and condensation products on environmental surfaces. The ability of ion trap SIMS to isolate and accumulate ions, and then perform tandem mass spectrometric analysis improves the detection of low-abundance surface contaminants and the selectivity of the technique. Utilizing these techniques, the limits of detection for HN-3 were studied as a function of surface coverage. It was found that HN-3 could be detected at a surface coverage of 0.01 monolayer, which corresponds to 20 ppm (mass/mass) for a soil having a surface area of 2.2 m(2) g(-1). TEA, the exhaustive hydrolysis product of HN-3, was detected at a surface coverage of 0.001 monolayer, which corresponds to 0.86 ppm.

Synthesis and cytotoxic activity of a glucuronylated prodrug of nornitrogen mustard

A new glucuronylated prodrug of nornitrogen mustard, incorporating the same spacer group as the doxorubicin prodrug HMR 1826, has been prepared. Upon exposure to E. coli beta-glucuronidase, fast hydrolysis occurs but a lower cytotoxicity against LoVo cancer cells is observed compared to the nornitrogen mustard alone. This is explained by cyclization of the intermediate carbamic acid to the inactive chloroethyl oxazolidinone.

Synthesis and antitumor activity of new benzoheterocyclic derivatives of distamycin A

The design, synthesis, and in vivo and in vitro antileukemic activity of a novel series of compounds (13-22 and 34), in which different benzoheterocyclic rings, bearing a nitrogen mustard or a benzoyl nitrogen mustard or an alpha-bromoacryloyl group as alkylating moieties, are tethered to a distamycin frame, are reported, and structure-activity relationships are discussed. The new derivatives were prepared by coupling nitrogen mustard-substituted, benzoyl nitrogen mustard-substituted, or alpha-bromoacryloyl-substituted benzoheterocyclic carboxylic acids 23-32 with desformyldistamycin (33) or in one case with its two-pyrrole analogue 35. With very few exceptions, the activities of compounds bearing the same alkylating moiety are slightly affected by the kind of the heteroatom present on the benzoheterocyclic ring. All novel compounds, with one exception, showed in vitro activity against L1210 murine leukemia cell line comparable to or better than that of tallimustine. The compounds in which the nitrogen mustard and the alpha-bromoacryloyl moieties are directly linked to benzoheterocyclic ring showed potent cytotoxic activities (IC(50) ranging from 2 to 14 nM), while benzoyl nitrogen mustard derivatives of benzoheterocycles showed reduced cytotoxic activities, and one compound (16) of this cluster was the sole derivative devoid of significant activity. Compound 18, a 5-nitrogen mustard N-methylindole derivative of distamycin, showed the best antileukemic activity in vivo, with a very long survival time (%T/C = 457), significantly increased in comparison to tallimustine (%T/C = 133), and was selected for further extensive evaluation. Arrested polymerase chain reaction and direct DNA fragmentation assays were performed for compound 18 and the structurally related compounds 13-17 and 19. The results obtained have shown that both alkylating groups and oligopeptide frames play a crucial role in the sequence selectivity of these compounds.

Structural analysis of the complex of a distamycin analogue with the Dickerson dodecamer 13C labeled at 5'-carbons using NMR spectroscopy

Structural analysis of the complex of a distamycin analogue (Tallimustine) with the Dickerson dodecamer d(C*G*C*G*A*A*T*T*C*G*C*G) [N*:[5'-(13)C]nucleotide] was performed by NMR spectroscopy and the results will be described in detail.

Molecular dynamics simulation of metallothionein-drug complexes

The intermolecular interactions of metallothionein with nitrogen mustard drugs were studied by molecular dynamics simulations. Previous laboratory experiments have defined selective alkylation of two cysteine residues, and selective binding was proposed to precede alkylation. The present study provides information about accessibility to cysteines based on evaluating the intermolecular energies and distances in the first few ps of dynamics simulations. A series of dynamics simulations was performed with three drug molecules positioned at the eight most solvent accessible cysteine residues of the dimeric form of the protein. Sites proximal to the sulfhydryl groups of Cys-33 and Cys-48 were found to be the most favorable for complexing the aziridinium forms of chlorambucil, melphalan, and mechlorethamine. The sites for preferential binding are in qualitative agreement with the sites of selective alkylation defined experimentally.