The early history of the biological alkylating agents, 1918-1968

Predictive validity in drug discovery: what it is, why it matters and how to improve it

Successful drug discovery is like finding oases of safety and efficacy in chemical and biological deserts. Screens in disease models, and other decision tools used in drug research and development (R&D), point towards oases when they score therapeutic candidates in a way that correlates with clinical utility in humans. Otherwise, they probably lead in the wrong direction. This line of thought can be quantified by using decision theory, in which 'predictive validity' is the correlation coefficient between the output of a decision tool and clinical utility across therapeutic candidates. Analyses based on this approach reveal that the detectability of good candidates is extremely sensitive to predictive validity, because the deserts are big and oases small. Both history and decision theory suggest that predictive validity is under-managed in drug R&D, not least because it is so hard to measure before projects succeed or fail later in the process. This article explains the influence of predictive validity on R&D productivity and discusses methods to evaluate and improve it, with the aim of supporting the application of more effective decision tools and catalysing investment in their creation.

The complexity and regulation of repair of alkylation damage to nucleic acids

DNA damaging agents have been a cornerstone of cancer therapy for nearly a century. The discovery of many of these chemicals, particularly the alkylating agents, are deeply entwined with the development of poisonous materials originally intended for use in warfare. Over the last decades, their anti-proliferative effects have focused on the specific mechanisms by which they damage DNA, and the factors involved in the repair of such damage. Due to the variety of aberrant adducts created even for the simplest alkylating agents, numerous pathways of repair are engaged as a defense against this damage. More recent work has underscored the role of RNA damage in the cellular response to these agents, although the understanding of their role in relation to established DNA repair pathways is still in its infancy. In this review, we discuss the chemistry of alkylating agents, the numerous ways in which they damage nucleic acids, as well as the specific DNA and RNA repair pathways which are engaged to counter their effects.

Evolution of Cancer Pharmacological Treatments at the Turn of the Third Millennium

The medical history of cancer began millennia ago. Historical findings of patients with cancer date back to ancient Egyptian and Greek civilizations, where this disease was predominantly treated with radical surgery and cautery that were often ineffective, leading to the death of patients. Over the centuries, important discoveries allowed to identify the biological and pathological features of tumors, without however contributing to the development of effective therapeutic approaches until the end of the 1800s, when the discovery of X-rays and their use for the treatment of tumors provided the first modern therapeutic approach in medical oncology. However, a real breakthrough took place after the Second World War, with the discovery of cytotoxic antitumor drugs and the birth of chemotherapy for the treatment of various hematological and solid tumors. Starting from this epochal turning point, there has been an exponential growth of studies concerning the use of new drugs for cancer treatment. The second fundamental breakthrough in the field of oncology and pharmacology took place at the beginning of the '80s, thanks to molecular and cellular biology studies that allowed the development of specific drugs for some molecular targets involved in neoplastic processes, giving rise to targeted therapy. Both chemotherapy and target therapy have significantly improved the survival and quality of life of cancer patients inducing sometimes complete tumor remission. Subsequently, at the turn of the third millennium, thanks to genetic engineering studies, there was a further advancement of clinical oncology and pharmacology with the introduction of monoclonal antibodies and immune checkpoint inhibitors for the treatment of advanced or metastatic tumors, for which no effective treatment was available before. Today, cancer research is always aimed at the study and development of new therapeutic approaches for cancer treatment. Currently, several researchers are focused on the development of cell therapies, anti-tumor vaccines, and new biotechnological drugs that have already shown promising results in preclinical studies, therefore, in the near future, we will certainly assist to a new revolution in the field of medical oncology.

Investigation of antigenotoxic potential of Syzygium cumini extract (SCE) on cyclophosphamide-induced genotoxicity and oxidative stress in mice

The present study investigated the protective effects of Syzygium cumini extract (SCE; 100 and 200 mg/kg) against genotoxicity and oxidative stress (OS) induced by cyclophosphamide (CP) in mice. Animals were received 14 days pretreatment (oral) of SCE, followed by induction of genotoxicity by CP (40 mg/kg), 24 hours before sacrifice. Mice bone marrow chromosomal aberration assay, micronucleus assay, and sperm abnormality assay were employed for the study. Activities of hepatic antioxidant enzymes were also investigated. Phytochemical investigation was done to determine total phenolic and flavonoid content in SCE. Results showed that CP produced a significant increase in average percentage of aberrant metaphases and chromosomal aberrations (CAs) excluding gap, and micronuclei (MN) formation in polychromatic erythrocytes produced cytotoxicity in mouse bone marrow cells and induced abnormal sperms in a male germ line. CP also markedly inhibited the activities of superoxide dismutase (SOD), catalase (CAT), and reduced glutahione (GSH) and increased malondialdehyde (MDA) content. Pretreatments with SCE significantly inhibited the frequencies of aberrant metaphases, CAs, MN formation, and cytotoxicity in mouse bone marrow cells induced by CP. SCE also produced a significant reduction of abnormal sperm and antagonized the reduction of CP-induced SOD, CAT, and GSH activities and inhibited increased MDA content in the liver. Total phenolic content present in SCE was 24.68%, whereas total flavonoids were calculated as 3.80%. SCE has a protective effect against genotoxicity and OS induced by CP.

Protective effects of eicosapentaenoic acid on genotoxicity and oxidative stress of cyclophosphamide in mice

The aim of this article is to elucidate the mechanism by which eicosapentaenoic acid (EPA) acts against cyclophosphamide (CP)-induced effects. The prevalence of micronuclei, the extent of lipid peroxidation, and the status of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) in both liver and serum of mice were used as intermediate biomarkers of chemoprotection. Lipid peroxidation and associated compromised antioxidant defenses (CAT and GPX) in CP treated mice were observed in the liver, serum, and were accompanied by increased prevalence of micronuclei in bone marrow. The number of MN was significantly different (p < 0.01) between the groups treated with CP (group III, IV, V, VI) and the solvent control (group II) (3.2 ± 0.7‰). There was a dose-dependent reduction in formation CP induced micronuclei by treatment with 100, 200, or 300 mg EPA/kg BW mice. Activities of SOD, CAT, and extent of lipid peroxidation were statistically different in liver cells of mice exposed to EPA only with CP compared with the CP group (group III). The present findings imply that EPA may be a potential antigenotoxic, antioxidant and chemopreventive agent and could be used as an adjuvant in chemotherapeutic applications.

[Cross-linked nucleic acids: formation, structure, and biological function]

Published data on the main types of reagents capable of introducing covalent interstrand cross links into nucleic acids (NA) are summarized in the present review. The reactivity of cross-linking agents, their preferred binding sites, and methods of determining the cross-link localization in a duplex are discussed. Cell response to DNA cross linking, namely, the blocking of replication and transcription, the initiation of reparation processes, and apoptotic death of the cell, are analyzed, as well as the use of cross-linking reagents in therapy and molecular biology.

Protective effects of total saponins from stem and leaf of Panax ginseng against cyclophosphamide-induced genotoxicity and apoptosis in mouse bone marrow cells and peripheral lymphocyte cells

BACKGROUND

Cyclophosphamide (CP), commonly used anti-cancer, induces oxidative stress and is cytotoxic to normal cells. It is very important to choice the protective agent combined CP to reduce the side effects in cancer treatment. Ginsenosides are biological active constituents of Panax ginseng C.A. Meyer that acts as the tonic agent for the cancer patients to reduce the side effects in the clinic application. Because CP is a pro-oxidant agent and induces oxidative stress by the generation of free radicals to decrease the activities of anti-oxidant enzymes, the protective effects of the total saponins from stem and leaf of P. ginseng C.A. Meyer (TSPG) act as an anti-oxidant agent against the decreased anti-oxidant enzymes, the genotoxicity and apoptosis induced by CP was carried out.

METHODS

The alkaline single cell gel electrophoresis was employed to detect DNA damage; flow cytometry assay and AO/EB staining assay were employed to measure cell apoptosis; the enzymatic anti-oxidants (T-SOD, CAT and GPx) and non-enzymatic anti-oxidant (GSH) were measured by the various colorimetric methods.

RESULTS

CP induced the significant DNA damage in mouse peripheral lymphocytes in time- and dose-dependent manners, inhibited the activities of T-SOD, GPx and CAT, and decreased the contents of GSH in mouse blood, triggered bone marrow cell apoptosis at 6 and 12h. TSPG significantly reduced CP-induced DNA damages in bone marrow cells and peripheral lymphocyte cells, antagonized CP-induced reduction of T-SOD, GPx, CAT activities and the GSH contents, decreased the bone marrow cell apoptosis induced by CP.

CONCLUSIONS

TSPG, significantly reduced the genotoxicity of CP in bone marrow cells and peripheral lymphocyte cells, and decreased the apoptotic cell number induced by CP in bone marrow cells. The effects of TSPG on T-SOD, GPx, CAT activities and GSH contents might partially contribute to its protective effects on CP-induced cell toxicities.

Chemoprotective effects of captopril against cyclophosphamide-induced genotoxicity in mouse bone marrow cells

The protective effects of captopril (CAP) against toxicity induced by cyclophosphamide (CP) in mice were investigated using the micronucleus assay for anticlastogenic activity in mouse bone marrow cells and liver glutathione (GSH) content. A single intraperitoneal (i.p.) injection of CAP at 50, 100, and 200 mg/kg 1 h prior to cyclophosphamide (50 mg/kg) reduced the frequency of micronucleated polychromatic erythrocytes (MnPCEs). All three doses of CAP significantly reduced the frequency of MnPCEs in mouse bone marrow compared to the group treated with CP alone (P<0.0001-0.01). CP significantly depleted the GSH content in liver but the application of CAP at a dose of 100 mg/kg 1 h before CP treatment repleted the GSH content. CAP exhibited concentration-dependent antioxidant activity, scavenging >96% of the 1,1-diphenyl-2-picryl hydrazyl free radicals when used at a concentration of 0.2 mM. It appears that CAP, due to its antioxidant activity and by increasing GSH levels, can modulate the reduced cellular thiol content induced by CP and reduce the genotoxicity of CP in bone marrow cells.

Flow cytometric detection of apoptotic bone marrow cells with fractional DNA content after application of WR-2721, cyclophosphamide, cisplatin, and exposure of mice to gamma rays

Little is known about the mechanisms of apoptosis triggered in normal cells of the haemopoietic system by the aminothiol WR-2721 (Amifostine), chemotherapeutic drugs, and ionizing radiation; thus, the present study was undertaken to evaluate the effects of WR-2721, cyclophosphamide (CP), cisplatin (CDDP), and 60Co gamma rays on induction of apoptotic DNA degradation in bone marrow cells. Adult male Swiss mice were treated with WR-2721 (400 mg/kg b.wt.), CP (200 mg/kg b.wt.), and CDDP (10 mg/kg b.wt.), and exposed to 6 Gy 60Co gamma rays. Alterations in the number of apoptotic cells with fractional DNA content and also the cell cycle position of the non-apoptotic cells were determined in the bone marrow at 7 and 24 hours after treatment of mice with these agents, using flow cytometric assay of the controlled extraction of low-MW DNA from apoptotic cells. The chemotherapeutic drugs CP and CDDP and 60Co gamma rays triggered apoptosis and affected the cell cycle position of the non-apoptotic cells in the mouse bone marrow. The pretreatment of mice with WR-2721 resulted in the modulatory action of the aminothiol on induction of apoptotic cell death and changes in the cell cycle distribution of the non-apoptotic cells caused by the DNA-damaging agents. The patterns of changes in the frequency of apoptotic cells and the cell cycle position of the non-apoptotic cells, observed in the bone marrow, were dependent on the agent(s) applied and the time interval after application of the drug(s) and exposure of mice to gamma rays. Understanding of the mechanisms responsible for triggering of apoptotic cell death and disturbing of the cell cycle by the DNA-damaging agents, and modulation of the apoptotic and cell cycle pathways by the aminothiol WR-2721, can lead to more effective therapy and chemo- and radio-protection of normal cells.

Flow cytometric estimation of the plasma membrane diversity of bone marrow cells in mice treated with WR-2721 and cyclophosphamide

The effects of S-2-/3-aminopropylamino/ethyl phosphorothioic acid (WR-2721, Amifostine) and cyclophosphamide (CP) on the cell surface exposure of phosphatidylserine (PS) and the plasma membrane impairment of bone marrow cells were assessed by flow cytometry assay with fluoresceinated annexin V (annexin V - FITC) and propidium iodide (PI). During the 96 h-period after treatment of adult male Swiss mice with WR-2721 (400 mg/kg b.wt.) and CP (200 mg/kg b.wt.), bone marrow cells expressing PS on the outer leaflet of the plasma membrane, which bound annexin V, and cells with a compromised cell membrane, which allowed PI to bind to the cellular DNA, were analysed. Temporary changes in the frequency of early apoptotic cells (annexin V - FITC positive/PI negative), late apoptotic and necrotic cells (annexin V - FITC positive/PI positive), and the number of live cells (annexin V - FITC negative/PI negative), were dependent on the drug(s) given. Application of CP distinctly triggered apoptotic and necrotic cell death, and WR-2721 pre-treatment of mice affected cell death induced by CP, causing reduction of the number of apoptotic and necrotic cells. The chemoprotective action of WR-2721 against PS externalisation and the plasma membrane impairment of normal bone marrow cells was shown.

Effects of GSH and WR-2721 on induction of micronuclei by cyclophosphamide

The frequency of micronucleated polychromatic erythrocytes (MNPCEs) was assessed in the bone marrow and peripheral blood of adult male Swiss mice treated with reduced glutathione (GSH) and/or S-2-/3-aminopropylamino/ethyl phosphorothioic acid (WR-2721), at a dose of 400 mg/kg body weight, and/or with cyclophosphamide (CP), at a dose of 200 mg/kg body weight. GSH was given 60 or 15 min and/or WR-2721 was applied 30 min before CP administration. The number of MNPCEs was determined at 24 h after the drug application. After treatment of mice with CP, the frequency of MNPCEs was distinctly increased. The stronger chemoprotective effect against CP-induced cytotoxicity was obtained following GSH administration than after WR-2721 injection. WR-2721 characterized greater cytotoxicity than GSH. The combination of GSH and WR-2721 given alone, or before CP administration resulted in the most cytotoxic and chemoprotective effects, compared with the respective single-thiol treatment of mice. The most effective protection against CP-induced genotoxicity was observed in the case of treatment of mice with WR-2721and GSH, respectively, 30 and 15 min before CP administration. The most cytotoxic effect of the thiols was found when GSH given 30 min prior to WR-2721 application. The chemoprotection and cytotoxicity caused in the mouse erythroblasts by GSH and WR-2721, as indicated by the number of MNPCEs were dependent on the thiol(s) given, and the time intervals between the drug administration. The modulatory effect of the thiols GSH and WR-2721 on 'delayed apoptosis' induced in the erythropoietic system by cyclophosphamide was shown.

An in vivo/in vitro method for assessing micronucleus and chromosome aberration induction in rat bone marrow and spleen. 2. Studies with chlorambucil and mitomycin C

An in vivo/in vitro system using rat bone marrow cells and spleen cells to assess micronucleus (MN) and structural chromosome aberrations (SCA) simultaneously (Moore et al., 1995) was further developed. In two separate experiments, two rats/dose/experiment were treated i.p. with 0, 5, 10 and 15 mg chlorambucil (CA)/kg or with mitomycin C (MMC) at 0, 1, 2, 4 mg/kg (experiment 1) or 0, 4, 6, and 8 mg/kg (experiment 2) and killed 6 h later. Cultures were then established in the presence of growth stimulants (interleukin-3 and granulocyte-macrophage colony stimulating factor for bone marrow; lipopolysaccharide and concanavalin A for spleen) and cytochalasin B, a cytokinesis inhibitor. Bone marrow cells were harvested 24 h after establishment of cultures, while spleen cells were harvested at 48 h. In addition, spleen cells were concurrently assayed for chromosome aberrations. With the MN endpoint, spleen cells appeared more sensitive than bone marrow cells to the effects of CA due both to a lower background and an increased response. For MMC, bone marrow cells exhibited both a higher background of MN and a greater numerical response than did spleen cells. However, on the basis of a fold-increase over control values, spleen cells were more sensitive than bone marrow cells. In general, the MN endpoint appeared more sensitive than the SCA in spleen cells after treatment with CA or MMC. Thus, the approach described here shows greater potential in detecting genotoxicity.

Nitrogen mustard inhibits transcription and translation in a cell free system

Nitrogen mustard and its derivatives such as cyclophosphamide, chlorambucil and melphalan are widely used anti-cancer agents, despite their non-specific reaction mechanism. In this study, the effect of alkylation by nitrogen mustard of DNA and RNA (coding for a single protein) was investigated using both a translation system and a coupled transcription/translation system. When alkylated DNA was used as the template for coupled transcription and translation, a single translation product corresponding to the 62 kDa luciferase protein was synthesised. Production of the translated product encoded by this template was inhibited by mustard concentrations as low as 10 nM, and 50% inhibition occurred with 30 nM mustard. A primer extension assay employed to verify alkylation sites on the DNA revealed that all guanine residues on the DNA template are susceptible to alkylation by nitrogen mustard. Similarly, when alkylated RNA was used as the template for protein synthesis, the amount of the 62 kDa luciferase protein decreased with increasing mustard concentration and a range of truncated polypeptides was synthesised. Under these conditions 50% inhibition of translation occurred with approximately 300 nM mustard (i.e. approximately 10 times that required for similar inhibition using an alkylated DNA template). Furthermore, a gel mobility shift assay revealed that mustard alkylation of the RNA template results in the formation of a more stable retarded RNA complex. The functional activity of the luciferase protein decreased with alkylation of both the DNA and RNA templates, with a half-life of loss of activity of 1.1 h for DNA exposed to 50 nM mustard, and 0.5 h for RNA exposed to 50 microM mustard. The data presented support the notion that DNA is a critical molecule in the mode of action of mustards.

Suppressing effect of WR-2721 on micronuclei induced by cyclophosphamide in mice

The effect of WR-2721 against cyclophosphamide-induced clastogenicity was studied using the in vivo micronucleus assay. The frequency of micronuclei in polychromatic erythrocytes in the peripheral blood of mice treated with WR-2721 and cyclophosphamide (CP), each of the compounds at a dose of 200 mg/kg body weight, was evaluated during the 15-day period. The suppressing effect of WR-2721, given 30 min prior to cyclophosphamide administration, on micronuclei induced by the alkylating agent was demonstrated. The number of micronuclei was increased on day 1 after CP application and declined thereafter with the frequency of micronucleated polychromatic erythrocytes remaining lower in WR-2721 pre-treated mice. The modulatory effect of WR-2721 on the clastogenic activity of cyclophosphamide in the erythropoietic system by the mouse micronucleus test was shown.

Inhibition of the clastogenic effect of cyclophosphamide by WR-2721 in the bone marrow of mice

The frequency of micronucleated polychromatic erythrocytes in the bone marrow of Swiss mice treated with WR-2721, at a dose of 200 mg/kg or 400 mg/kg body weight, 15 or 30 min prior to cyclophosphamide (CP) administration, at a dose of 200 mg/kg body weight, was determined 24 h after CP treatment. In mice injected with CP, the number of micronuclei in polychromatic erythrocytes was significantly increased in comparison with the controls, and in mice treated with WR-2721 and CP, the frequency of micronucleated polychromatic erythrocytes was distinctly decreased in comparison to those given CP alone. The protective effect of WR-2721 against cyclophosphamide-induced clastogenicity was shown. The effect was dependent on the dose of the thiol agent given, and it was more expressed when WR-2721 was applied at the higher dose, 400 mg/kg body weight. However, the protection by the aminothiol appeared not to depend on the time intervals between WR-2721 and CP administration to the mouse organism.

Analysis of the malondialdehyde-2'-deoxyguanosine adduct in rat liver DNA by gas chromatography/electron capture negative chemical ionization mass spectrometry

Malondialdehyde (MDA), a product of lipid peroxidation, causes mutations in bacterial and mammalian cells and cancer in rats. MDA reacts with deoxynucleosides in vitro and the monomeric adduct of MDA with deoxyguanosine (M1G-dR) is the major adduct formed. We have developed a sensitive analytical method to characterize and quantify M1G-dR from biological matrices using gas chromatography/electron capture negative chemical ionization mass spectrometry (GC/ECNCI MS). Reduction of M1G-dR with sodium borohydride produced a dihydro derivative (H2-M1G-dR). This more stable analog had improved high-performance liquid chromatographic characteristics which facilitated its isolation from biological fluids. H2-M1G-dR was converted to a monopentafluorobenzyl derivative with simultaneous depurination; it was then converted to the corresponding t-butyldimethylsilyl derivative and analyzed by GC/ECNCI MS. (2H2)H2-M1G was used as internal standard. Quantitative analysis was carried out using selected ion monitoring of m/z 302 and m/z 304 where the limit of detection was 10 pg (30 fmol) injected on-column. The level of M1G-dR in normal rat liver was 5.2 +/- 0.2 modified bases per 10(7) bases (n = 6 rats).

Effect of alkylating agents on initiation and elongation of the lac UV5 promoter

DNA containing the lac UV5 promoter was alkylated using bifunctional sulfur and nitrogen mustards and a monofunctional sulfur mustard. The alkylation sites were mapped using Taq polymerase, and the effect of alkylation on the formation of the DNA-RNA polymerase complex was determined using gel retardation. Alkylation was observed at all G residues in the template strand. Exposure of the alkylated DNA to Escherichia coli RNA polymerase resulted in the formation of a DNA-enzyme complex that was more stable, prior to initiation, than the complex formed with nonalkylated DNA. The DNA-RNA polymerase complex formed with the alkylated DNA also demonstrated decreased ability to progress along the full length of the DNA template. These observations show that, in addition to inducing transcriptional blockages, mustards also influence the interaction between RNA polymerase and its promoter. The ability to interfere with protein-DNA interactions may contribute significantly to the effects of these compounds in eukaryotic systems with their complex array of transcription factors.

DNA-directed aniline mustards based on 9-aminoacridine: interaction with DNA

A series of 4-substituted aniline mustards ArNH(CH2)nOpC6H4N(CH2CH2Cl)2, where Ar is an acridine and n varies from 2 to 5, interact with DNA. Scatchard analysis shows the compounds bind tightly, with a binding site size similar to that of 9-aminoacridine. The rate of hydrolysis of the mustards, measured by HPLC, is essentially constant across the series. With increasing length of the polymethylene linker, non-covalent binding becomes less strong, but the rate of DNA alkylation increases. Viscometric helix extension measurements and electrophoretic analyses using closed circular supercoiled DNA show that all the compounds are DNA intercalating ligands. Despite these similarities, the compounds are known to have quite different patterns of DNA alkylation, switching from guanine to adenine alkylation as the chain length is extended.

Preferential induction of AT-TA transversion, but not deletions, by chlorambucil at the hisG428 site of Salmonella typhimurium TA102

The chemotherapeutic agent chlorambucil effectively induces deletion mutations in mouse germ cells. The possibility that this chemical also effectively induces deletion mutations in bacterial DNA was examined using Ames Salmonella tester strains. Chlorambucil was mutagenic only to strains TA102 (hisG428, rfa/pKM101) and YG2975 (hisG46, rfa/pKM101) when S9 mix was absent. Since strain TA102 can detect short deletions, the mutational changes of TA102 induced by this agent without S9 mix were directly determined by the DNA sequencing technique. It turned out that chlorambucil did not induce deletion mutations but preferentially induced AT-TA transversions at the hisG428 site of plasmid pAQ1 of strain TA102. These results caution that the positive results induced by chlorambucil in mutagenicity tests do not necessarily mean the occurrence of deletions.