Synthesis, DNA-binding properties, and antitumor activity of novel distamycin derivatives

Therapeutic gene regulation using pyrrole-imidazole polyamides

Recent innovations in cutting-edge sequencing platforms have allowed the rapid identification of genes associated with communicable, noncommunicable and rare diseases. Exploitation of this collected biological information has facilitated the development of nonviral gene therapy strategies and the design of several proteins capable of editing specific DNA sequences for disease control. Small molecule-based targeted therapeutic approaches have gained increasing attention because of their suggested clinical benefits, ease of control and lower costs. Pyrrole-imidazole polyamides (PIPs) are a major class of DNA minor groove-binding small molecules that can be predesigned to recognize specific DNA sequences. This programmability of PIPs allows the on-demand design of artificial genetic switches and fluorescent probes. In this review, we detail the progress in the development of PIP-based designer ligands and their prospects as advanced DNA-based small-molecule drugs for therapeutic gene modulation.

Synthesis and biological activity of benzamide DNA minor groove binders

A range of di- and triaryl benzamides were synthesised to investigate the effect of the presence and nature of a polar sidechain, bonding and substitution patterns and functionalisation of benzylic substituents. These compounds were tested for their antiproliferative activity as well as their DNA binding activity. The most active compounds in all assays were unsymmetrical triaryl benzamides with a bulky or alkylating benzylic substituent and a polar amino sidechain.

Design, synthesis and biological evaluation of novel sesquiterpene mustards as potential anticancer agents

Several novel series of sesquiterpene mustards (SMs) bearing nitrogen mustard and glutathione (GSH)-reactive α-methylene-γ-butyrolactone groups were successfully prepared for the first time and showed excellent antiproliferative activities in vitro. Among them, compounds 2e and 2g displayed the highest antiproliferative properties with IC50 values ranging from 2.5 to 8.7 μM. The selectivity of these two compounds was evaluated by SRB method against human cancer and normal hepatic cells (HepG2 and L02). The induction of apoptosis and effects on the cell cycle distribution with compounds 2e and 2g were investigated by Hoechst 33,258 staining and flow cytometry, which exhibited that they could induce selective cell apoptosis and cell cycle arrest in HepG2 and L02 cells. In addition, further investigation showed that compounds 2e and 2g could obviously inhibit the proliferation of HepG2 cells by inducing significant DNA cross-linking and depleting GSH in cell media. The good cytotoxicity and selectivity of compounds 2e and 2g pointed them as promising leads for anticancer drug design.

Resistance to minor groove binders

In this paper multiple resistance mechanisms to minor groove binders (MGBs) are overviewed. MGBs with antitumor properties are natural products or their derivatives and, as expected, they are all substrates of P-glycoprotein (P-gp). However, a moderate expression of P-gp does not appear to reduce the sensitivity to trabectedin, the only MGB so far approved for clinical use. Resistance to this drug is often related to transcriptional mechanisms and to DNA repair pathways, particularly defects in transcription-coupled nucleotide excision repair (TC-NER). Therefore tumors resistant to trabectedin may become hypersensitive to UV rays and other DNA damaging agents acting in the major groove, such as Platinum (Pt) complexes. If this is confirmed in clinic, that will provide the rationale to combine trabectedin sequentially with Pt derivates.

Minor groove binders as anti-infective agents

Minor groove binders are small molecules that form strong complexes with the minor groove of DNA. There are several structural types of which distamycin and netropsin analogues, oligoamides built from heterocyclic and aromatic amino acids, and bis-amidines separated by aromatic and heterocyclic rings are of particular pharmaceutical interest. These molecules have helical topology that approximately matches the curvature of DNA in the minor groove. Depending upon the precise structure of the minor groove binder, selectivity can be obtained with respect to the DNA base sequence to which the compound binds. Minor groove binders have found substantial applications in anti-cancer therapy but their significance in anti-infective therapy has also been significant and is growing. For example, compounds of the bis-amidine class have been notable contributors to antiparasitic therapy for many years with examples such as berenil and pentamidine being well-known. A recent growth area has been inreased sophistication in the oligoamide class. High sequence selectivity is now possible and compounds with distinct antibacterial, antifungal, antiviral, and antiparasitic activity have all been identified. Importantly, the structures of the most active compounds attacking the various infective organisms differ significantly but not necessarily predictively. This poses interesting questions of mechanism of action with many different targets involved in DNA processing being candidates. Access of compounds to specific cell types also plays a role and in some cases, can be decisive. Prospects for a range of selective therapeutic agents from this class of compounds are higher now than for some considerable time.

From multiply active natural product to candidate drug? Antibacterial (and other) minor groove binders for DNA

Natural products that bind to DNA in the minor groove are valuable templates for drug design. Examples include distamycin, netropsin, duocarmycin and anthramycin. Anticancer and anti-infective drugs feature strongly amongst their derivatives. The structures and activities of chemotypes with various therapeutic actions are discussed in the context of the broader field of therapeutically active minor groove binders. The evolution of a series of exceptionally potent and nontoxic antibacterial compounds is discussed using the general design principle of introducing additional hydrophobicity into the distamycin template to increase the strength of binding to DNA. As well as potent antibacterial compounds, antifungal and antiparasitic compounds with exceptional cellular activity against trypanosomes have been identified. Possible mechanisms of action including gene regulation and topoisomerase inhibition are discussed with the need in mind to understand selective toxicity in the series to support future drug discovery.

Fifty years of chemical research at Farmitalia

This review contains a brief description of the chemistry developed in Farmitalia and, after 1978, Farmitalia-Carlo Erba Research Laboratories, during the second half of the last century. It gives an overview of work that represents a significant part of the chemistry carried out in Italy during this period in the field of medicinal and natural product chemistry. This is particularly true when we consider in addition to the work done intramurally in the said laboratories, the work done by academic scientists in the frame of the various extramural collaborations. Only a fraction of the chemical research actually carried out is reported here as time and space dictated a selection. Subjects typically associated with Farmitalia and which gave rise to important scientific or therapeutic outcomes are given preference in this review.

Mass spectrometry studies of the binding of the minor groove-directed alkylating agent alkamin to AT-tract oligonucleotides

Minor groove binding alkylating agents, which have potential as cancer drugs, generate cytotoxic DNA adducts that are relatively resistant to repair as a consequence of locating covalent attachment at purine N3 nitrogen atoms. Recently, we used electrospray and matrix-assisted laser desorption ionization mass spectrometry to study the binding of the minor groove-directed polybenzamide bis-half-mustard alkamin, and its monofunctional analogue alkamini, to the oligonucleotide d(CGCGAATTCGCG)(2), identifying a number of inter- and intrastrand alkamin cross-links involving the GAATTC sequence [ Abdul Majid , A. M. S. , Smythe , G. , Denny , W. A. , and Wakelin , L. P. G. ( 2007 ) Mol. Pharmacol. 71 , 1165 - 1178 ]. Here, we extend these studies to d(CGCAAATTTGCG)(2), A3T3, and d(CGCAAAAAAGCG).d(CGCTTTTTTGCG), A6/T6, in which the opportunity for both inter- and intrastrand cross-linking is enhanced. We find that both ligands alkylate all adenines in the longer AT-tracts, as well as the abutting guanines, whether they are in the same strand as the adenines or not, in a manner consistent with covalent attack on purine N3 atoms from the minor groove. Alkamin forms intrastrand cross-links involving A4 and A6 and A6 and G10 in A3T3 and all of the purines in the A6/T6 purine tract, including G10. In addition, it forms interstrand cross-links between A4, A5, A6 and A4', A5', A6', between G10 and the latter adenines in A3T3, and between G22 and adenines A5 and A6 in A6/T6. The reactivity of the abutting guanines provides unexpected opportunities for both inter- and intrastrand cross-linking by alkamin, such as the interstrand cross-link in the CAAAAAAG sequence. We conclude that positioning monofunctional mustard groups on either end of a minor groove-directed polybenzamide has the capacity to enhance interstrand cross-links at all manner of AT-tracts, including most in which the adenines are all in one strand.

Binding to the minor groove of the double-strand, tau protein prevents DNA from damage by peroxidation

Tau, an important microtubule associated protein, has been found to bind to DNA, and to be localized in the nuclei of both neurons and some non-neuronal cells. Here, using electrophoretic mobility shifting assay (EMSA) in the presence of DNA with different chain-lengths, we observed that tau protein favored binding to a 13 bp or a longer polynucleotide. The results from atomic force microscopy also showed that tau protein preferred a 13 bp polynucleotide to a 12 bp or shorter polynucleotide. In a competitive assay, a minor groove binder distamycin A was able to replace the bound tau from the DNA double helix, indicating that tau protein binds to the minor groove. Tau protein was able to protect the double-strand from digestion in the presence of DNase I that was bound to the minor groove. On the other hand, a major groove binder methyl green as a negative competitor exhibited little effect on the retardation of tau-DNA complex in EMSA. This further indicates the DNA minor groove as the binding site for tau protein. EMSA with truncated tau proteins showed that both the proline-rich domain (PRD) and the microtubule-binding domain (MTBD) contributed to the interaction with DNA; that is to say, both PRD and MTBD bound to the minor groove of DNA and bent the double-strand, as observed by electron microscopy. To investigate whether tau protein is able to prevent DNA from the impairment by hydroxyl free radical, the chemiluminescence emitted by the phen-Cu/H₂O₂/ascorbate was measured. The emission intensity of the luminescence was markedly decreased when tau protein was present, suggesting a significant protection of DNA from the damage in the presence of hydroxyl free radical.

The usefulness of cyclic diamidines with different core-substituents as antitumor agents

A series of related polycationic compounds has been screened for potential antitumor activity by the NCI's in vitro testing (one dose primary anticancer assay and the NCI-60 full panel screening). The GI50 values of triazines 3 and 4 are on average 1.9 microM and 2.4 microM, respectively. Furan 8 deserves mention too (1.9 microM). The biological test results showed that carbazole 10 possessed cytotoxic activity in the nanomolar range, much better than the other compounds tested, only against several cancer cell lines: CCRF-CEM, HL-60(TB), MOLT-4, NCI-H522, COLO 205, SF-268, but the average GI50 value was higher (15 microM). The activity appears closely dependent on the core-shape and length of the bisimidazoline molecules (important for both high cytotoxicity and DNA binding). The mechanism of DNA minor-groove binding of diamidines 1-12, based on the anticancer parameters, is highly probable.

Anticancer drug discovery and pharmaceutical chemistry: a history

There are several procedures for the chemical discovery and design of new drugs from the point of view of the pharmaceutical or medicinal chemistry. They range from classical methods to the very new ones, such as molecular modeling or high throughput screening. In this review, we will consider some historical approaches based on the screening of natural products, the chances for luck, the systematic screening of new chemical entities and serendipity. Another group comprises rational design, as in the case of metabolic pathways, conformation versus configuration and, finally, a brief description on available new targets to be carried out. In each approach, the structure of some examples of clinical interest will be shown.

Novel Bcl-2 Inhibitors: Discovery and Mechanism Study of Small Organic Apoptosis-Inducing Agents

Apoptosis as a novel target for cancer chemotherapy has generated an intense demand for new apoptosis-inducing agents. The newly revealed role of protein families involved in the apoptosis pathway, and resistance to cytotoxic therapies have opened new avenues for the development of novel anticancer strategies. We have established a novel strategy to rapidly obtain protein-targeted, instead of conventional DNA-targeted, apoptosis inducers as antitumor leads. First, a novel organic non-DNA intercalative compound S1 (8-oxo-3-thiomorpholin-4-yl-8H-acenaphtho[1,2-b]pyrrole-9-carbonitrile, M(W) = 331) was found with an IC50 of 10(-7)-10(-8) microM against diverse cancer cell lines. Further biological evaluation demonstrated that it was an apoptosis-inducer both in vivo and in vitro. The treatment of hydroperitoneum hepatoma cells (H22 cell line) with S1 at various concentrations (from 0.01 to 10 microM) for 24 h triggered these cells to enter the apoptosis process. The antitumor efficiency was also tested in the H22 xenotransplant models in mice. At a dosage of 0.3 mg kg(-1), S1 exhibited significant antitumor activity with a much longer survival time, a decrease in tumor size, and increased apoptosis cells in tumor tissue. More importantly, studies of the molecular mechanism of apoptosis induction by S1 revealed that S1 inactivated the Bcl-2 protein by binding to it, depolarizing the mitochondrial membrane, and then activating caspase 9, followed by caspase 3. Finally, structure-based virtual modification was performed by computer modeling. As a result, a derivative, S2 (8-oxo-3-[(thienylmethyl)amino]-8H-acenaphtho[1,2-b]pyrrole-9-carbonitrile, M(W) = 341) was identified that possessed a lower binding energy to Bcl-2, and demonstrated better antitumor potency, even on the Bcl-2-overexpressing human acute myeloid leukemia (HL-60) cells (IC50 = 1.3 microM) in vitro. S1 and S2 are the well-defined Bcl-2 inhibitors that give us a promising platform for the development of new therapeutic agents.

Potent antitumor 9-anilinoacridines bearing an alkylating N-mustard residue on the anilino ring: synthesis and biological activity

A series of N-mustard derivatives of 9-anilinoacridine was synthesized for antitumor and structure-activity relationship studies. The alkylating N-mustard residue was linked to the C-3' or C-4' position of the anilino ring with an O-ethylene (O-C(2)), O-butylene (O-C(4)), and methylene (C(1)) spacer. All of the new N-mustard derivatives exhibited significant cytotoxicity in inhibiting human lymphoblastic leukemic cells (CCRF-CEM) in culture. Of these agents, (3-(acridin-9-ylamino)-5-{2-[bis (2-chloroethyl)amino]ethoxy}phenyl)methanol (10) was subjected to antitumor studies, resulting in an approximately 100-fold more potent effect than its parent analogue 3-(9-acridinylamino)-5-hydroxymethylaniline (AHMA) in inhibiting the growth of human lymphoblastic leukemic cells (CCRF-CEM) in vitro. This agent did not exhibit cross-resistance against vinblastine-resistant (CCRF-CEM/VBL) or Taxol-resistant (CCRF-CEM/Taxol) cells. Remarkably, the therapeutic effect of 10 at a dose as low as one tenth of the Taxol therapeutic dose [i.e., 1-2mg/kg (Q3Dx7) or 3mg/kg (Q4Dx5); intravenous injection] on nude mice bearing human breast carcinoma MX-1 xenografts resulted in complete tumor remission in two out of three mice. Furthermore, 10 yielded xenograft tumor suppression of 81-96% using human T-cell acute lymphoblastic leukemia CCRF-CEM, colon carcinoma HCT-116, and ovarian adenocarcinoma SK-OV-3 tumor models.

Cinnamoyl nitrogen mustard derivatives of pyrazole analogues of tallimustine modified at the amidino moiety: design, synthesis, molecular modeling and antitumor activity studies

The design, synthesis and in vitro activities of a series of cinnamoyl nitrogen mustard pyrazole analogues of tallimustine 8-13, in which the amidino moiety has been replaced by moieties of different physico-chemical features are described, and the structure-activity relationships are discussed. In spite of the relevance of these modifications on the amidino moiety, these derivatives showed significant growth inhibitory activity against mouse leukemia L1210 cells. A selected series of compounds have been evaluated for their sequence selective alkylating properties and cytotoxicity against human K562 leukemia cells. Therefore, the presence of the amidino moiety, and in general of a basic moiety, is not an absolute requirement for biological activity. Our preliminary results indicated that the compounds of this series have a pattern of alkylation similar to that of tallimustine, but they seem to be less reactive overall in alkylating naked DNA.

A novel class of achiral seco-analogs of CC-1065 and the duocarmycins: design, synthesis, DNA binding, and anticancer properties

The synthesis, DNA binding properties, and in vitro and in vivo anticancer activity of fifteen achiral seco-cyclopropylindoline (or achiral seco-CI) analogs (5a-o) of CC-1065 and the duocarmycins are described. The achiral seco-CI analogs contain a 4-hydroxyphenethyl halide moiety that is attached to a wide range of indole, benzimidazole, pyrrole, and pyridyl-containing noncovalent binding components. The 4-hydroxyphenethyl halide moiety represents the simplest mimic of the seco-cyclopropylpyrroloindoline (seco-CPI) pharmacophore found in the natural products, and it lacks a chiral center. The sequence and minor groove specificity of the achiral compounds was ascertained using a Taq DNA polymerase stop assay and a thermal induced DNA cleavage experiment using either a fragment of pBR322 or pUC18 plasmid DNA. For example, seco-CI-InBf (5a) and seco-CI-TMI (5c) demonstrated specificity for AT-rich sequences, particularly by reacting with the underlined adenine-N3 position of 5'-AAAAA(865)-3'. This is also the sequence that CC-1065 and adozelesin prefer to alkylate. The achiral seco-CI compounds were subjected to cytotoxicity studies against several human (K562, LS174T, PC3, and MCF-7) and murine cancer cell lines (L1210 and P815). Following continuous drug exposure, the achiral compounds were found to be cytotoxic, with IC(50) values in the muM range. Interestingly, the carbamate protected compound 5p was significantly less cytotoxic than agent 5c, supporting the hypothesis that loss of HCl and formation of a spiro[2,5]cyclopropylcyclohexadienone intermediate is necessary for biological activity. The achiral seco-CI compounds 5a and 5c were submitted to the National Cancer Institute for further cytotoxicity screening against a panel of 60 different human cancer cell lines. Both compounds showed significant activity, particularly against several solid tumor cell lines. Flow cytometry studies of P815 cells that were incubated with compound 5c at its IC(50) concentration for 24h showed induction of apoptosis in a large percentage of cells. Compounds 5a and 5c were selected by the NCI for an in vivo anticancer hollow-fiber test, and received composite scores of 18 and 22, respectively. These two compounds were subsequently evaluated for in vivo anticancer activity against the growth of a human advanced stage SC UACC-257 melanoma in skid mice. At a dose of 134 mg/kg administered IP, compound 5c gave a T/C value of 40% (for day 51), and the median number of days of doubling tumor growth was 27.7, versus 15.8 for untreated animals. For compound 5a, at 200mg/kg, the T/C was 58% and the median number of days of doubling tumor growth was 20.0 versus 8.7 for untreated animals. At these doses no toxicity or weight loss was observed for either compound. Furthermore, compound 5c was not toxic to murine bone marrow cell growth in culture, at a dose that was toxic for the previously reported seco-CBI (cyclopropylbenzoindoline)-TMI (4).

Synthesis and biological evaluation of new cyclic amidine analogs of chlorambucil

A number of novel cyclic amidine analogs of chlorambucil were synthesized and examined for cytotoxicity in breast cancer cell cultures and for inhibition of topoisomerases I and II. Evaluation of the cytotoxicity of these compounds employing a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and inhibition of [(3)H]-thymidine incorporation into DNA in both MDA-MB-231 and MCF-7 breast cancer cells demonstrated that these compounds were more active than chlorambucil. The degree to which these compounds inhibited cell growth breast cancer cells was directly correlated to DNA-binding affinity. These studies indicate that cyclic amidine analogs of chlorambucil are a potent catalytic inhibitor of topoisomerase II but not topoisomerase I. The highest degree of DNA binding and cytotoxicity in both MDA-MB-231 and MCF-7 breast cancer cells was observed for the compound, which possess a 4,5-dihydro-1H-imidazol moiety.

Synthesis and biological evaluation of novel diaziridinylquinone–acridine conjugates

The synthesis and biological evaluation of a homologous series of conjugates (9-13) of 2,5-diaziridinylbenzoquinone (DZQ) and 9-carbonylacridine, a DNA intercalating moiety, via a polymethylene unit (n=2-6) are described. In addition, the non-acridine compound 14, analogous to compound 12, and the 5-methyl-DZQ derivatized conjugate 15, an analog of compound 10, were also prepared. Through a Comet assay, compounds 9-13 were shown to produce DNA interstrand cross-links at submicromolar concentrations, consistent with K562 leukemia cells accumulating in the G2/M stage in the cell cycle. The cytotoxicity of compounds 9-15 was examined using a MTT assay on several human cancer cell lines, including chronic myeloid leukemia K562, the non-small cell lung cancers H596 and H460, and colon carcinoma cells BE and HT29. H460 and HT29 are rich in DT-diaphorase (DTD), and H596 and BE cells have negligible amounts of functional DTD. Under continuous exposure of drugs, except to the non-aziridine compound 19b, the IC50 values of all other compounds were determined to be in the range of 0.3-11.3 nM. Compound 10, which has a propyl linker group, was subjected to in vivo studies. When BDF1 mice with established mouse mammary carcinoma were treated with compound 10 (2 mg/kg at day 1 and 5 mg/kg at day 7), a significant delay (9-10 days) in cancer growth was recorded when compared to untreated controls. Furthermore, administration of compound 10 to nu/nu BDF1 mice bearing human lung cancer H460 xenograft (1.5 mg/kg for 10 for five consecutive days from day 13 and 17) also showed a significant reduction in tumor growth compared to untreated controls. The half-life of compound 10 in the presence of five different peptidases (porcine esterase, carboxypeptidase A, B and Y, and pepsin) was determined to be between 30 and 60 h.

Synthesis and preliminary cytotoxicity of nitrogen mustard derivatives of distamycin A

Distamycin and nitrogen mustard conjugates, in which the nitrogen mustard unit was coupled to the C-terminus of the pyrrole, were synthesized. The switching of the nitrogen mustard unit from the N-terminus to the C-terminus did not compromise the compound's cytotoxicity. Compound 3, bearing three pyrrole units, was highly toxic to human K562 leukemia cells in vitro with an IC(50) value of 0.03 microM. Addition of a trans double bond to the molecule had little effects on cytotoxicity.

DNA: still a target worth aiming at? A review of new DNA-interactive agents

DNA acts as the final target for most clinically effective cytotoxic agents, but the lack of selectivity for tumor cells has raised questions about the value of developing new DNA-interactive agents. Three new classes of cytotoxic agents are reviewed; each interacts directly with DNA but cytotoxicity appears to be mediated through novel mechanisms, including the interaction with specific proteins by DNA-bound drug molecules. Irofulven is the lead compound of the illudin family of molecules. It causes a novel type of DNA damage whose repair is dependent on functioning DNA helicases. Pre-clinical and clinical synergy between irofulven and agents which inhibit topoisomerases has been observed. Clinical trials with irofulven have shown significant activity and phase II studies in pancreatic, ovarian and prostatic cancer are ongoing. Toxicity in the form of myelosuppression and fatigue have been shown to be schedule dependent, with intermittent administration appearing to significantly reduce toxicity. DNA-interacting agents which alkylate bases exposed in the minor groove have been derived from a number of natural sources. The minor groove alkylation appears to be sequence specific; although the significance of this specificity for cytotoxicity is unclear, one proposed mechanism is through inhibition of expression of particular genes. Three cyclopropylpyrroloinole analogues which cause sequence specific minor groove alkylation are currently under clinical assessment. Myelosuppression is the dose limiting toxicity and is biphasic in its time course. Moderate activity in phase I trials has been observed. Ecteinascidins represent one of the increasing number of groups of drugs isolated from marine organisms. Ecteinascidin-743 (ET-743) is the most advanced in its clinical development. Binding to the minor groove of DNA occurs, although with a different base specificity from other compounds. The cytotoxic effects of ET-743 may occur by inhibition of the inducible transcription of a number of genes by sequestration of specific transcription factors. Clinical trials of ET-743 have shown significant activity, and phase II trials are underway in soft tissue sarcoma and breast cancer. Hepatic toxicity and myelosuppression are predictable and appear associated with peak plasma concentrations, whereas efficacy seems to be improved with prolonged infusion.

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.

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.

Cytotoxic halogenoacrylic derivatives of distamycin A

The design, synthesis, in vitro and in vivo activities of a series of halogenoacrylic derivatives of distamycin A are described. The structure-activity relationships indicate a key role of the reactivity of alpha-halogenoacrylic moiety. The reactivity and the putative alkylating mechanism of these compounds are different from those of the nitrogen mustards and possibly based on a Michael type reaction. This supports the hypothesis that these compounds represent a class of minor groove binders mechanistically different from tallimustine.

Sequence specific alkylation of DNA by hairpin pyrrole-imidazole polyamide conjugates

BACKGROUND

Pyrrole-imidazole polyamides are synthetic ligands that recognize predetermined sequences in the minor groove of DNA with affinities and specificities comparable to those of DNA-binding proteins. As a result of their DNA-binding properties, polyamides could deliver reactive moieties for covalent reaction at specific DNA sequences and thereby inhibit DNA-protein interactions. Site-specific alkylation of DNA could be a useful tool for regulating gene expression. As a minimal first step, we set out to design and synthesize a class of hairpin polyamides equipped with DNA alkylating agents and characterize the specificity and yield of covalent modification.

RESULTS

Bis(dichloroethylamino)benzene derivatives of the well-characterized chlorambucil (CHL) were attached to the gamma turn of an eight-ring hairpin polyamide targeted to the HIV-1 promoter. We found that a hairpin polyamide-CHL conjugate binds and selectively alkylates predetermined sites in the HIV promoter at subnanomolar concentrations. Cleavage sites were determined on both strands of a restriction fragment containing the HIV-1 promoter, revealing good specificity and a high yield of alkylation.

CONCLUSIONS

The ability of polyamide-CHL conjugates to sequence specifically alkylate double-stranded DNA in high yield and at low concentrations sets the stage for testing their use as regulators of gene expression in cell culture and ultimately in complex organisms.

Mitomycin C linked to DNA minor groove binding agents: synthesis, reductive activation, DNA binding and cross-linking properties and in vitro antitumor activity

Mitomycin C (MC) is a natural cytotoxic agent used in clinical anticancer chemotherapy. Its antitumor target appears to be DNA. Upon bioreductive activation MC alkylates and cross-links DNA. MC derivatives were synthesized in which MC was linked to DNA minor groove binding agents, analogous to netropsin and distamycin. One, two and three N-methylpyrrole carboxamide units were conjugated with MC by a (CH2)5-tether to the 7-amino group of MC (11, 12 and 13, respectively). In contrast to MC 11, 12 and 13 displayed non-covalent affinity to DNA. Their bioreductive activation by NADPH-cytochrome c reductase proceeded as fast as that of MC. Metabolites arising from reductive and low-pH activation were characterized and found to be analogous to those of MC. DNA cross-linking activities were weak and decreased with an increasing number of N-methylpyrrole carboxamide units linked with the mitomycin molecule. No adducts were formed with calf thymus DNA in detectable amounts. In vitro antitumor activities of 11-13 were determined using the NCI in vitro antitumor screen. The conjugates 11-13 are growth inhibitory; however, their activities are 1.5-2 orders of magnitude lower than that of MC. COMPARE analysis indicates that the mechanism of the action of 11 and 12 correlates moderately with MC but negatively with distamycin. Conjugate 13 correlates neither with MC nor with distamycin. The results suggest that the basic cause of the observed low activity of the MC-minor groove binder conjugates is the fast irreversible decay of the activated MC, competing effectively with the slow drug delivery to CpG sites, required for the alkylation.

Novel benzoyl nitrogen mustard derivatives of pyrazole analogues of distamycin A: synthesis and antileukemic activity

The design and synthesis of novel benzoic acid mustard (BAM) derivatives of distamycin A bearing one or more pyrazole rings replacing the pyrrole rings of the latter are described. In vitro and in vivo activities against L1210 leukemia are reported and discussed. Some of these compounds show an activity profile comparable to tallimustine 1. All the compounds bearing the pyrazole ring close to the BAM moiety show reduced cytotoxicity in comparison to derivatives characterized by the BAM linked to a pyrrole: the same effect has not been observed when occurring at the amidine terminus of the oligopeptidic frame.

DNA minor-groove binders: results and design of new antitumor agents

DNA minor-groove binding drugs have been extensively studied in the last years in order to influence the regulation of gene expression in neoplastic disorders by means of specific interactions with DNA bases. Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs), CC-1065 and distamycins are three classes of minor-groove alkylating agents which showed interesting cytotoxicity profiles, but they cannot be used in humans for various toxicity problems. For this reason many groups applied heterocyclic substitutions extensively, in order to either modify the reactivity profile or introduce extra interactions within the minor groove, thus changing the binding site or modulating the binding sequence.

Responsiveness to hormone, growth factor and drug treatment of a human breast cancer cell line: comparison between early and late cultures

Growth rate, morphology, and responsiveness to mitogenic stimuli and pharmacological treatments were evaluated in early and late cell passages derived from the same clone of the widely used MCF-7 human breast adenocarcinoma cell line. Our results indicate dissimilarities between early (E) and late (L) passages for some of the parameters analyzed. The cells that underwent many subcultivations grew faster than the others; both appeared homogeneous in size and shape. The E cells, subcultured for almost 1 yr, displayed higher sensitivity to the mitogenic action of both estradiol, according to the level of estrogen receptor, and insulin-like growth factor-I than did the L cells, kept in culture for more than 10 yr. Cell responsiveness to two drugs, a novel steroid antiestrogen and a polysulfonated distamycin A derivative, was more pronounced in the early cultures only at the longer time of exposure to the higher concentration of the estrogen antagonist. In addition, a drug-induced inhibition of insulin-like growth factor-I binding to its receptor was shown in both E and L cells, the latter being less sensitive than the former when exposed to the antiestrogen. Finally, MCF-7 E and L cells showed similar behavior when drug-induced apoptosis was tested.

Distamycin-A derivatives potentiate tumor-necrosis-factor activity via the modulation of tyrosine phosphorylation

The cytotoxic activities of 2 novel distamycin-A derivatives, FCE 24517 and FCE 25450A, alone and in combination with tumor-necrosis factor-alpha (TNF), were studied. Both drugs, especially FCE 25450A, analyzed extensively here, inhibited the growth of HL60 promyelocytic cells, and human SV80 and murine L929 transformed fibroblasts in a dose-dependent manner. The growth-inhibitory potential of sequential exposure to the distamycin-A analogs and TNF was determined. A 4-hr treatment of L929 fibroblasts with 100-1,000 ng/ml FCE 25450A, followed by 2 ng/ml TNF, resulted in a synergistic anti-proliferative effect. The synergism of FCE 24517 with TNF was less profound. Experiments to elucidate the mechanism underlying the cooperation revealed that FCE 25450A pre-treatment almost completely abolished the elevated tyrosine phosphorylation of a 137-kDa and other membranal proteins and prevented the de-phosphorylation of another protein band observed in L929 cells in the presence of TNF. FCE 25450A alone induced no changes in the phosphotyrosine profile of the cells. The effect of FCE 25450A was counteracted by the tyrosine-phosphatase inhibitor orthovanadate. In parallel, the inhibitor also diminished the antiproliferative action of the FCE 25450A/TNF combination. These findings suggest that, beyond their cytotoxic effects as single agents, the distamycin derivatives increase the sensitivity of cells to TNF. This effect is governed via the inhibition of TNF-induced tyrosine phosphorylation of specific proteins which are probably involved in the development of TNF resistance. Thus, protein de-phosphorylation might provide an additional mechanism of action of these novel distamycin-A-derived drugs.

Structure-activity relationship of a series of C-terminus modified aminoalkyl, diaminoalkyl- and anilino-containing analogues of the benzoic acid mustard distamycin derivative tallimustine: synthesis, DNA binding and cytotoxicity studies

As part of our investigations into the design of more cytotoxic analogues of the experimental anticancer drug tallimustine, 1, C-terminus modified aminoalkyl-, 2a-c, diaminoalkyl-, 3, and anilino-containing, 4, derivatives have been synthesized. Compounds 2a-c differ by 2, 3, or 4 methylene units in the C-terminus, respectively. Results from an ethidium displacement study on poly(dA-dT), poly(dG-dC), calf thymus DNA and T4 coliphage DNA showed that compounds 2-4 interact in the minor groove of the polynucleotides with a preference for poly(dA-dT) over poly(dG-dC). Compound 4 bound more weakly to the DNAs than 2a-c and 3. Using a CD dilution assay compounds 2a-c and 3 were demonstrated to bind irreversibly to calf thymus DNA. The sequence selectivity by which compounds 2-4 alkylate DNA was demonstrated using a Taq polymerase stop assay. All the compounds alkylated preferentially at the 3'-purine residue in a 5'-TTTTGPu-3' sequence (Pu = A or G). This observed sequence specificity is similar to that of tallimustine and a related compound 5. At an equimolar concentration the aminoalkyl compounds 2a-c (2b > 2a > 2c), and diaminoalkyl compound 3 were more efficient at alkylating these sequences than the anilino compound 4. Following a one hour exposure of human chronic myeloid leukemia K562 cells, compounds 2b and 3 have lower IC50 values (1.64 microM and 3.03 microM, respectively) than tallimustine (5 microM) and similar values to a related compound 5 (2.2 microM). The order of cytotoxicity for all the compounds is 2b > 5 > 3 > 2a > 1 > 2c = 4. These results indicate that the cytotoxicities of these compounds are related to their relative ability to alkylate the consensus DNA binding sequence.

The sequence specificity of alkylation for a series of benzoic acid mustard and imidazole-containing distamycin analogues: the importance of local sequence conformation

The covalent sequence specificity of a series of nitrogen mustard and imidazole-containing analogues of distamycin was determined using modified sequencing techniques. The analogues tether benzoic acid mustard (BAM) and possess either one, two or three imidazole units. Examination of the alkylation specificity revealed that BAM produced guanine-N7 lesions in a pattern similar to conventional nitrogen mustards. The monoimidazole-BAM conjugate also produced guanine-N7 alkylation in a similar pattern to BAM, but at a 100-fold lower dose. The diimidazole and triimidazole conjugates did not produce detectable guanine-N7 alkylation but only alkylated at selected sites in the minor groove. Unexpectedly, the alkylation specificity at equivalent doses was nearly identical to that found for the previously reported pyrrole-BAM conjugates. The consensus sequence, 5'-TTTTGPuwas strongly alkylated by the triimidazole conjugate in preference to other similar sites including three occurrences of 5'-TTTTAA. Footprinting studies were carried out to examine the non-covalent DNA binding interactions. These studies revealed that the tripyrrole- BAM conjugate bound non-covalently to the same AT-rich sites as distamycin. In contrast, whereas the Im3lexitropsin bound non-covalently to GC-rich sequences, the triimidazole-BAM conjugate did not detectably footprint to either GC- or AT-rich regions at equivalent doses. The results indicate that the alkylation event is not solely dictated by the non-covalent binding and might be influenced by a unique sequence dependent conformational feature of the consensus sequence 5'-TTTTGPu.

Anti-insulin-like growth factor-I activity of a novel polysulphonated distamycin A derivative in human lung cancer cell lines

1. The purpose of this study was to investigate the antiproliferative effect and the modulation of the mitogenic insulin-like growth factor-I (IGF-I) system by FCE 26644 and FCE 27784, two polyanionic sulphonated distamycin A derivative compounds, on two human non-small cell lung cancer (N-SCLC) cell lines. 2. For cell growth studies the colorimetric MTT and the thymidine incorporation assays were performed; the presence of IGF-I and IGF-binding proteins in conditioned media was revealed by radioimmunoassay and Western ligand blot, respectively. Variations at the IGF-I-receptor level were tested by binding studies on cell monolayers. 3. A significant concentration- and time-dependent cytostatic activity of FCE 26644 (IC50 approximately 200 micrograms ml-1 at 72 h) compared to its analogue FCE 27784 (IC50 > 800 micrograms ml-1) was observed in both cell lines studied. The IGF-I-stimulated proliferation of the IGF-I-responsive A549 cell line was abolished by 24 h of FCE 26644 treatment whereas FCE 27784 was inactive. FCE 26644 increased (4 to 6 fold) the secretion of IGF-I-like material and reduced the IGF-I binding (IC50 > 100 micrograms ml-1) in both A549 and Ca-Lu-1 cell lines. FCE 26644 (100 micrograms ml-1) did not affect the KD (approximately 0.5 nM) but reduced the Bmax and the number of receptor sites (50%). 4. Our findings demonstrate that the ability to down-regulate the cell proliferation of N-SCLC cell lines, shown by FCE 26644, depends at least partially, on interference with the "IGF-I mitogenic system'.

Treatment with inhibitors of polyamine biosynthesis, which selectively lower intracellular spermine, does not affect the activity of alkylating agents but antagonizes the cytotoxicity of DNA topoisomerase II inhibitors

Inhibitors of ornithine decarboxylase (ODC), such as alpha-difluoromethylornithine (DFMO), may influence the cytotoxicity of anti-tumour agents that interact with DNA. Intracellular levels of putrescine and spermidine were markedly reduced by ODC inhibitors while the level of spermine, which is the main polyamine in nuclei, was unchanged. By combining a novel inhibitor of ODC, such as (2R, 5R)-6-heptyne-2,5-diamine (MDL 72.175, MAP), with an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), such as 5'-[[(Z)-4-aminobut-2-enyl]methylamino]-5'-deoxyadenosine (MDL 73.811, AbeAdo), spermine was selectively depleted in a human ovarian cancer cell line OVCAR-3 (i.e. spermine became almost undetectable whereas the levels of spermidine and putrescine were not affected). The depletion of spermine blocked DNA synthesis with a consequent accumulation of cells in the G1 phase of the cell cycle. Pretreatment with MAP plus AbeAdo did not change the cytotoxicity of alkylating agents, such as L-phenylalanine mustard (L-PAM), 1,4-bis(2'-chloroethyl)-1,4-diazabicyclo-[2.2.1] heptane diperchlorate (DABIS), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), cis-diamminedichloroplatinum (II) (cis-DDP), N-deformyl-N-[4-N-N,N-bis (2-chloroethylamino)benzoyl] (tallimustine) or CC-1065, whereas it markedly reduced the cytotoxicity of DNA topoisomerase II inhibitors, such as doxorubicin (DX) and 4'-demethylepipodophyllotoxin-5-(4,6-O)-ethylidene- beta-D-glycopyranoside (VP-16). The addition of spermine before drug treatment restored the sensitivity to the DNA topoisomerase II inhibitors, thus indicating that the reduced effect was related to the intracellular spermine level. The reason for the reduction in cytotoxicity is unclear, but it does not appear to be related to a cell cycle effect or to a decrease in the intracellular level of DNA topoisomerase II. Drugs that modify polyamine biosynthesis are under early clinical development as potential new anti-tumour agents. These findings illustrate the need for caution in combining such drugs with DNA topoisomerase II inhibitors.