Uptake and cytotoxicity of novel nitroimidazole-polyamine conjugates in Ehrlich ascites tumour cells

l,8-Naphthalimide based DNA intercalators and anticancer agents. A systematic review from 2007 to 2017

In this review, we describe a detailed investigation about the structural variations and relative activity of 1,8-naphthalimide based intercalators and anticancer agents. The 1,8-naphthalimides binds to the DNA via intercalation, and exert their antitumor activities through Topoisomerase I/II inhibition, photoinduced DNA damage or related mechanism. Here, our discussion focused on works published over the last ten years (2007-2017) related to therapeutic applications, in the order of cancer treatment followed by other properties of 1,8-naphthalimides. In preparing for this review, we considered that several seminal reviews have appeared over the last fifteen years and focused on closely related subjects, however, none of them is exhaustive.

F14512, a polyamine-vectorized inhibitor of topoisomerase II, exhibits a marked anti-tumor activity in ovarian cancer

Epithelial ovarian cancer is the fourth cause of death among cancer-bearing women and frequently associated with carboplatin resistance, underlining the need for more efficient and targeted therapies. F14512 is an epipodophylotoxin-core linked to a spermine chain which enters cells via the polyamine transport system (PTS). Here, we investigate this novel concept of vectorization in ovarian cancer. We compared the effects of etoposide and F14512 on a panel of five carboplatin-sensitive or resistant ovarian cancer models. We assessed the incorporation of F17073, a spermine-linked fluorescent probe, in these cells and in 18 clinical samples. We then showed that F14512 exhibits a high anti-proliferative and pro-apoptotic activity, particularly in cells with high levels of F17073 incorporation. Consistently, F14512 significantly inhibited tumor growth compared to etoposide, in a cisplatin-resistant A2780R subcutaneous model, at a dose of 1.25 mg/kg. In addition, ex vivo analysis indicated that 15 out of 18 patients presented a higher F17073 incorporation into tumor cells compared to normal cells. Overall, our data suggest that F14512, a targeted drug with a potent anti-tumor efficacy, constitutes a potential new therapy for highly PTS-positive and platinum-resistant ovarian cancer-bearing patients.

Current status of the polyamine research field

This chapter provides an overview of the polyamine field and introduces the 32 other chapters that make up this volume. These chapters provide a wide range of methods, advice, and background relevant to studies of the function of polyamines, the regulation of their content, their role in disease, and the therapeutic potential of drugs targeting polyamine content and function. The methodology provided in this new volume will enable laboratories already working in this area to expand their experimental techniques and facilitate the entry of additional workers into this rapidly expanding field.

Preclinical activity of F14512, designed to target tumors expressing an active polyamine transport system

We have exploited the polyamine transport system (PTS) to deliver selectively a spermine-drug conjugate, F14512 to cancer cells. This study was aimed to define F14512 anticancer efficacy against tumor models and to investigate whether fluorophor-labeled polyamine probes could be used to identify tumors expressing a highly active PTS and that might be sensitive to F14512 treatments. Eighteen tumor models were used to assess F14512 antitumor activity. Cellular uptake of spermine-based fluorescent probes was measured by flow cytometry in cells sampled from tumor xenografts by needle biopsy. The accumulation of the fluorescent probe within B16 tumors in vivo was assessed using infrared fluorescence imaging. This study has provided evidence of a major antitumor activity for F14512. Significant responses were obtained in 67% of the tumor models evaluated, with a high level of activity recorded in 33% of the responsive models. Complete tumor regressions were observed after i.v., i.p. or oral administrations of F14512 and its antitumor activity was demonstrated over a range of 2-5 dose levels, providing evidence of its good tolerance. The level of cellular fluorescence emitted by the fluorescent probes was higher in cells sampled from tumors sensitive to F14512 treatments than from F14512-refractory tumors. We suggest that these probes could be used to identify tumors expressing a highly active PTS and guide the selection of patients that might be treated with F14512. These results emphasize the preclinical interest of this novel molecule and support its further clinical development.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

Structure-activity investigations of polyamine-anthracene conjugates and their uptake via the polyamine transporter

A series of polyamine conjugates were synthesized and evaluated for their ability to target the polyamine transporter (PAT) in two Chinese hamster ovary (CHO) cell lines (PAT-active CHO and PAT-inactive CHOMG). This systematic study identified salient features of the polyamine architecture required to target and enter cells via the PAT. Indeed, the separation of charges, the degree of N-alkylation, and the spacer unit connecting the N(1)-terminus to the appended cytotoxic component (anthracene) were found to be key contributors to optimal delivery via the PAT. Using the CHO screen, the homospermidine motif (e.g., 4,4-triamine) was identified as a polyamine vector, which could enable the selective import of large N(1)-substituents (i.e., naphthylmethyl, anthracenylmethyl and pyrenylmethyl), which were cytotoxic to cells. The cell selectivity of this approach was demonstrated in B-16 murine melanoma cells and normal melanocytes (Mel-A). Three polyamine areas (recognition and transport, vesicle sequestration and polyamine-target interactions) were identified for future research.

Polyamine-Substituted Gadolinium Chelates: A New Class of Intracellular Contrast Agents for Magnetic Resonance Imaging of Tumors

A new class of intracellular contrast agents (CA) for magnetic resonance imaging has been developed, based on Gd(DTPA) with two positively charged amide-linked substituents. Uptake of Gd(DTPA) into cultured tumor cell lines (B16 mouse melanoma, MH3924A Morris hepatoma) was below the detection limit while CA with the melanin-binding pharmacophore 2-(diethylamino)ethylamine reached intracellular concentrations of ca. 0.03 fmol/cell (ca. 20 microM) for melanoma and 0.02 fmol/cell for hepatoma (24 h at 10 microM CA). With the polyamine substituents bis(2-aminoethyl)amine or spermidine, CA uptake increased up to 3-fold for melanoma (0.083 fmol/cell) and 9-fold for hepatoma (0.18 fmol/cell). Uptake of polyamine-substituted CA was reduced by the polyamine transport inhibitor benzyl viologen. Molar relaxivities for three Gd-DTPA-polyamine complexes were in the range 5.6-6.9 for the free complex in solution and 7.7-23.5 s-1 mM-1 for Morris hepatoma cell pellets. T1-weighted magnetic resonance imaging at 2.35 T of rats with MH3924A tumors showed contrast enhancement in tumor at 1 and 24 h postinjection of polyamine-substituted CA.

Biological Properties of IDN5174, a New Synthetic Camptothecin with the Open Lactone Ring

A series of water-soluble camptothecins obtained by linking a spermidine moiety to the 21-position of the open form through an amidic bond have been tested for their biochemical and biological activities. Growth inhibition assay on the human non-small cell lung cancer carcinoma NCI-H460 cell line revealed that the camptothecin analogues were less potent than topotecan and SN38 after 1 hour of treatment. The potency increased after 72 hours of exposure, being similar to that of reference camptothecins. The analysis of topoisomerase I-mediated DNA cleavage using the purified enzyme indicated that the novel camptothecin analogues retained ability to poison topoisomerase I and displayed the same cleavage pattern of SN38. Persistence of the DNA cleavage was comparable with that of SN38. Stabilization of the cleavable complex was not the result of hydrolysis of the N-C bond between polyamine and the drug because no free camptothecin was recovered at the end of DNA cleavage in presence of IDN5174, the analogue selected for detailed studies. IDN5174 exhibited an antitumor activity comparable with that of topotecan and irinotecan against NCI-H460 tumor xenograft. The pharmacokinetics in mice showed a favorable disposition in tumor tissue with low amount of camptothecin detectable in plasma and tumor (around 5-10%), thus supporting the efficacy of intact IDN5174. In conclusion, we found that IDN5174 maintained the biological and antitumor properties, in spite of lack of the closed E ring. The available results support the interpretation that the polyamine linked at the 21-position may allow a favorable drug interaction in the ternary complex.

Synthesis and Cytotoxic Activity of Polyamine Analogues of Camptothecin

A number of derivatives of camptothecin with a polyamine chain linked to position 7 of camptothecin via an amino, imino, or oxyiminomethyl group were synthesized and tested for their biological activity. All compounds showed marked growth inhibitory activity against the H460 human lung carcinoma cell line. In particular, the iminomethyl derivatives where the amino groups of the chain were protected with Boc groups exhibited a high potency, with IC50 values of approximately 10(-8) M. The pattern of DNA cleavage in vitro and the persistence of the cleavable ternary complex drug-DNA-topoisomerase I observed with polyamine conjugates containing free amino groups support a contribution of specific drug interaction with DNA as a determinant of activity. Modeling of compound 7c in the complex with topoisomerase 1 and DNA is consistent with this hypothesis. The lack of a specific correlation between stabilization of the cleavable complex and growth inhibition likely reflects multiple factors including the cellular pharmacokinetic behavior related to the variable lipophilicity of the conjugate, and the nature and linkage of the polyamine moiety.

Fluorophor-labeled spermidine derivatives as fluorescent markers in optical tumor imaging

Up-regulation of polyamine transporters on the surface of tumor cells and the internalization of biogenic polyamines by active transport processes may be exploited for the accumulation of spermidine derivatives as reporter molecules. We have synthesized and tested fluorophor-labeled spermidine derivatives for the development of a new class of intraoperative tumor imaging agents. In vitro uptake experiments and initial in vivo imaging studies illustrated that fluorophor tagged spermidine derivatives show tumor accumulation.

Antizyme induction mediates feedback limitation of the incorporation of specific polyamine analogues in tissue culture

Spermidine, spermine and putrescine are essential for mammalian cell growth, and there has been a pervasive effort to synthesize analogues of these polyamines that will disrupt their function and serve as tools to inhibit cell proliferation. Recently, we demonstrated that a number of such polyamine analogues are also capable of inducing the regulatory protein AZ (antizyme). In the present study the incorporation of a few sample analogues [mimics of bis(ethyl)spermine] was shown to be significantly limited by a decrease in the V(max) for the polyamine transport system in response to analogue-induced AZ. This creates an unusual circumstance in which compounds that are being designed for therapeutic use actually inhibit their own incorporation into targeted cells. To explore the impact of this feedback system, cultures of rat hepatoma HTC cells were pre-treated to exhibit either low or high polyamine uptake activity and then exposed to polyamine analogues. As predicted, regardless of initial uptake activity, all cultures eventually achieved the same steady-state levels of the cellular analogue and AZ. Importantly, analogue-induced AZ levels remained elevated with respect to controls even after the native polyamines were reduced by more than 70%. To model the insufficient AZ expression found in certain tumours, GS-CHO (GS Chinese-hamster ovary) cells were transfected to express high levels of exogenic AZI (AZ inhibitor). As anticipated, this clone incorporated significantly higher levels of the polyamine analogues examined. This study reveals a potential limitation in the use of polyamine-based compounds as therapeutics, and strategies are presented to either circumvent or exploit this elegant transport feedback system.

Effect of spermine conjugation on the cytotoxicity and cellular transport of acridine

Polyamines are believed to be potent vectors for the selective delivery of chemotherapeutic agents into cancer cells. In this paper, we report the effect of spermine conjugation on the cytotoxic and transport properties of acridine. Six derivatives, composed of a spermine chain attached at its N(1) position to an acridine via an aliphatic chain, were synthesized. The aliphatic linker, comprised of 3-5 methylene units, was connected to the position-9 of the heterocycle through either an amide (amidoacridines 8-10) or an amine (aminoacridines 11-13) linkage. Independently of their architecture, all ligands showed a high affinity for DNA binding but a limited DNA sequence selectivity. In a whole cell assay with L1210 and Chinese hamster ovary (CHO) cells, the aminoacridines (IC(50) values around 2 microM) were more potent than the amidoacridines (IC(50) values between 20 and 40 microM). This was related to a less efficient transport for the latter. As determined from competitive uptake studies with [(14)C]spermidine, all conjugates had a high affinity for the polyamine transport system (PTS). However, on the basis of competitive studies with an excess of spermidine and on the differential effect on cell growth and accumulation in CHO and in the mutant PTS deficient CHO-MG cells, the accumulation of the conjugates through the PTS was found to be poor but still more efficient for the aminoacridines. alpha-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, which induces an up-regulation of the activity of the PTS, enhanced accumulation of all acridine conjugates through the PTS and had a synergistic effect on the potency of the acridine conjugates to inhibit cell growth. Despite their high affinity for the PTS, the low amount of derivatives transiting through the PTS is likely to be related to their ability to repress rapidly and efficiently the activity of the PTS and, consequently, to inhibit their own uptake via this system.

N-Benzylpolyamines as vectors of boron and fluorine for cancer therapy and imaging: synthesis and biological evaluation

Cancer cells have high-affinity polyamine uptake systems with a low stringency for structural features. Putrescine, spermidine, and spermine have, therefore, been considered as potential vectors for the selective accumulation in tumors of therapeutically or diagnostically useful structures and elements. We envisaged N-benzyl derivatives of the polyamines as vectors of (10)B and (18)F for boron neutron capture therapy (BNCT) and tumor imaging by positron emission tomography (PET), respectively. In the present work, the synthesis, transport characteristics, DNA-binding properties, and cytotoxicity of several N-benzyl derivatives of putrescine and spermidine are described. The fluorinated spermidine derivative N-(3-[(4-aminobutyl)amino]propyl)[(4-fluorophenyl)methyl]amine (N(1)-4-Fbz-spd) may be useful for PET because of its high accumulation in cancer cells via the polyamine transport system. Among the boron-containing benzyl polyamines, N-(4-aminobutyl)([4-(dihydroxyboryl)phenyl]methyl)amine (4-Bbz-put) and N-(3-[(4-aminobutyl)amino]propyl)([4-(dihydroxyboryl)phenyl]methyl)amine (N(1)-4-Bbz-spd) should be suitable for BNCT, because their accumulation in B16 melanoma cells was more efficient than that of borocaptate and borophenylalanine, two reference compounds used in BNCT.

Polyamine sulfonamides with NMDA antagonist properties are potent calmodulin antagonists and cytotoxic agents

N1-Dansylspermine and related sulfonamides of the natural polyamines are very potent blockers of NMDA-type glutamate receptors. They exhibit pharmacological properties which were not predicted from the constituents of the conjugates. Cytotoxicity and calmodulin antagonism of N1-dansylspermine were especially impressive. Calmodulin antagonism implies that N1-dansylspermine prevents induction of ornithine decarboxylase and inhibits its own active uptake via the polyamine transport system. Structure-activity considerations demonstrated that an aromatic character of the substituent is not required; amide bond formation with an aliphatic sulfonic acid is sufficient to transform spermine into a highly toxic calmodulin antagonist. Cytotoxicity and calmodulin antagonism are properties which are intrinsic to spermine, but they are observed only at very high concentrations. Amide bond formation at N1 with a lipophilic residue appears to 'amplify' these normally latent properties. The use of polyamine conjugates structurally related to the amides described in this work for targeting tumours may be marred by their calmodulin antagonism.

Characterization of simian malarial parasite (Plasmodium knowlesi)-induced putrescine transport in rhesus monkey erythrocytes. A novel putrescine conjugate arrests in vitro growth of simian malarial parasite (Plasmodium knowlesi) and cures multidrug resistant murine malaria (Plasmodium yoelii) infection in vivo

A stage-dependent increase in the level of putrescine, spermidine, and spermine during intraerythrocytic growth of Plasmodium knowlesi in rhesus monkey erythrocytes was observed. Further, intraerythrocytic P. knowlesi-induced putrescine influx was found in trophozoite stage-infected erythrocytes and process was time- and temperature-dependent and showed saturable kinetics. Characteristics of induced putrescine influx appears in infected erythrocytes to be close to the normal erythrocytes in terms of affinity of putrescine to the putrescine transporter (Km 34.6 +/- 3.8 microM as normal erythrocytes and Km 37.2 +/- 5.2 microM in infected erythrocytes). However, the difference involves the significant increase in the putrescine influx rate after infection (Vmax = 4.21 nmol/min/10(10) normal erythrocytes, compared with 11.6 nmol/min/10(10) infected erythrocytes). Energy dependence, involvement of -SH group, and noninterference by amino acid, spermidine, and spermine in the putrescine influx process clearly demonstrate the presence of a distinct transporter for putrescine in infected erythrocytes. A putrescine conjugate N1,N4-bis(7-chloroquinoline-4-yl)butane-1, 4-diamine (BCBD) was synthesized, which inhibits the putrescine influx in the P. knowlesi infected erythrocytes (Ki of 43.2 microM) as well as in vitro growth of P. knowlesi (IC50 value, 7.64 +/- 0.97 ng/ml BCBD, 10.8 +/- 0.45 ng/ml chloroquine). Addition of exogenous polyamines failed to reverse the inhibitory effect of BCBD in vitro. Administration of BCBD (24 mg/kg body weight, intraperitoneal, twice a day for 4 days) cured the Swiss mice infected with multidrug-resistant infection of Plasmodium yoelii. Therefore, inhibition of putrescine transport in malaria-infected erythrocytes offers a lead in the search of a new class of chemotherapeutic molecules against malaria.

Polyamine transport in mammalian cells. An update

The uptake and release of the natural polyamines putrescine, spermidine and spermine by mammalian cells are integral parts of the systems that regulate the intracellular concentrations of these biogenic amines according to needs. Although a general feature of all tissues, polyamine uptake into intestinal mucosa cells is perhaps the most obvious polyamine transport pathway of physiological and pathophysiological importance. Mutant cell lines lacking the ability to take up polyamines from the environment are capable of releasing polyamines. This indicates that uptake and release are functions of two different transport systems. The isolation of a transporter gene from a mammalian cell line is still lacking. Overaccumulation of polyamines is controlled by release and by a feedback regulation system that involves de novo synthesis of antizyme, a well known protein that also regulates the activity of ornithine decarboxylase. Recent work has demonstrated that Ca(2+)-signalling pathways are also involved. Although there is consensus about the importance of polyamine uptake inhibitors in the treatment of neoplastic disorders, a practically useful uptake inhibitor is still missing. However, the attempts to target tumours, and to increase the selectivity of cytotoxic agents by combining them with the polyamine structure, are promising. New, less toxic and more selective anticancer drugs can be expected from this approach.