Toxicities derived from anti-tumor screening data

Niacin esters of chalcones with tumor-selective properties

Novel series of niacin esters of chalcones 2, 4 and 6 were designed as antineoplastic agents that have the potential to release the chemoprotectant niacin. These enones are cytotoxic to human CD4(+ )T-lymphocyte Molt 4/C8 and CEM and murine leukemia L1210 cells. Quantitative structure-activity relationship (QSAR) studies of the biodata in series 4 revealed that cytotoxic potency was enhanced by placing electron-repelling groups in one of the aryl rings. The compounds are lethal to HL-60, HSC-2, HSC-3 and HSC-4 neoplasms but less toxic to nonmalignant hepatocyte growth factor, hematopoietic progenitor cell and human periodontal ligament fibroblast cells. Hence, the compounds display tumor-selective toxicity. These chalcones are well tolerated in mice and no overt toxicity was noted. The results establish that in general the compounds in series 2, 4 and 6 have positive characteristics which warrant further studies.

3,5-Bis(benzylidene)-1-[3-(2-hydroxyethylthio)propanoyl]piperidin-4-ones: a novel cluster of potent tumor-selective cytotoxins

Novel 3,5-bis(benzylidene)-1-[3-(2-hydroxyethylthio)propanoyl]piperidin-4-ones (3a-e) display potent cytotoxicity and a preferential lethality toward various neoplasms compared to some normal cells. The corresponding sulfonic acid analogues 5a-e and an isostere 4 demonstrated substantially lower activity. The leads 3d and 3e possess very high activity against colon cancer and leukemia cell lines, caused DNA fragmentation, and activated caspase-3 in HL-60 cells. The enones 3b-e were well tolerated in a short-term toxicity screen in mice.

1,3-diaryl-2-propenones and 2-benzylidene-1,3-indandiones: a quest for compounds displaying greater toxicity to neoplasms than normal cells

A series of 1,3-diaryl-2-propenones 2a-j and analogous 2-benzylidene-1,3-indandiones 3a-j were evaluated against various neoplasms and normal cells. In general, greater cytotoxic potencies and selective toxicity to human malignant cells were observed by the compounds in series 2 rather than 3. In particular, 2i emerged as a lead molecule having an average CC(50) figure of 8.6 µM and a selective index value of 18. Various physicochemical features of 2a-j were correlated with the cytotoxic potencies to neoplastic cell lines which provide guidelines for expansion of this series of compounds. The enone 2i induced internucleosomal DNA fragmentation and activated caspase-3 in HL-60 cells suggesting that one of the ways in which the cytotoxicity of the compounds in series 2 is mediated towards some of the cell lines used in this study is by apoptosis. Neurotoxicity in mice was generally lower in series 2 than 3a-j.

Haemotoxicity of busulphan, doxorubicin, cisplatin and cyclophosphamide in the female BALB/c mouse using a brief regimen of drug administration

Many anticancer drugs are myelotoxic and cause bone marrow depression; however, generally, the marrow/blood returns to normal after treatment. Nevertheless, after the administration of some anti-neoplastic agents (e.g. busulphan, BU) under conditions as yet undefined, the marrow may begin a return towards normal, but normality may not be achieved, and late-stage/residual marrow injury may be evident. The present studies were conducted to develop a short-term mouse model (a 'screen') to identify late-stage/residual marrow injury using a brief regimen of drug administration. Female BALB/c mice were treated with BU, doxorubicin (DOX), cisplatin (CISPLAT) or cyclophosphamide (CYCLOPHOS) on days 1, 3 and 5. In 'preliminary studies', a maximum tolerated dose (MTD) for each drug was determined for use in 'main studies'. In main studies, mice were treated with vehicle (control), low and high (the MTD) dose levels of each agent. Necropsies were performed, and blood parameters and femoral/humeral nucleated marrow cell counts (FNCC/HNCC) were assessed on six occasions (from days 1 to 60/61 post-dosing). Late-stage/residual changes were apparent in BU-treated mice at day 61 post-dosing: RBC, Hb and haematocrit were reduced, mean cell volume/mean cell haemoglobin were increased and platelet and FNCC counts were decreased. Mice given DOX, CISPLAT and CYCLOPHOS, in general, showed no clear late-stage/residual effects (day 60/61). It was concluded that a brief regimen of drug administration, at an MTD, with assessment at day 60/61 post-dosing was a suitable short-term method/screen in the mouse for detecting late-stage/residual marrow injury for BU, a drug shown to exhibit these effects in man.

Cytotoxic 2-benzylidene-6-(nitrobenzylidene)cyclohexanones which display substantially greater toxicity for neoplasms than non-malignant cells

Various 2-benzylidene-6-(nitrobenzylidene)cyclohexanones were prepared as candidate cytotoxins in which the nitro group was located in the ortho, meta and para positions leading to series 1-3, respectively. The CC(50) values towards human HSC-2 and HSC-4 oral squamous cell carcinomas as well as human HL-60 promyelocytic leukemic cells are in the low micromolar range in general. On the other hand, most of the compounds afforded clear evidence of being far less toxic towards human HGF gingival fibroblasts, HPC pulp cells and HPLF periodontal ligament fibroblasts which are non-malignant cells. Selectivity index (SI) figures were generated which are the ratios of the average CC(50) values towards normal cells and the CC(50) figure towards a malignant cell line. Huge SI values were obtained for many of the compounds. In particular 1c, 2f, 3c and 3g which have average SI values of >76, >38, 124 and 341, respectively, are clearly lead molecules affording direction for amplification of this area of study. A lead compound 1c caused internucleosomal DNA fragmentation and activation of caspase-3 in HL-60 cells but not in HSC-2 carcinomas. In a short-term toxicity study, doses up to and including 300 mg/kg of the majority of the compounds prepared in this study did not cause any mortalities to mice. Some guidelines for development of these tumor-selective cytotoxins are presented.

1,5-diaryl-3-oxo-1,4-pentadienes: a case for antineoplastics with multiple targets

A number of organic molecules which contain the 1,5-diaryl-3-oxo-1,4-pentadienyl group, referred to hereafter as the dienone moiety, have antineoplastic properties. Emphasis is made on the attachment of this structural moiety to several molecular scaffolds, namely piperidines, N-acylpiperidines, cycloalkanes and 3,4-dihydro-1H-napthalenes. Many of these compounds are potent cytotoxins having micromolar and nanomolar IC(50) values towards a wide range of neoplastic and transformed cells. On occasions, greater toxicity towards neoplasms than normal cells has been demonstrated. A number of these compounds have in vivo anticancer properties and in general excellent tolerability in rodents is demonstrated. The way in which a number of physicochemical properties such as redox potentials, torsion angles, atomic charges and logP values govern cytotoxic potencies are presented. The importance of the shapes of different compounds as determined by molecular modeling in contributing to antineoplastic properties is outlined. Arguments are presented in favour of designing antineoplastics which have multiple sites of action in contrast to those bioactive molecules which have only one molecular target. A number of compounds which possess the dienone group have different modes of action some of which are chronicled in this review, such as inducing apoptosis, affecting respiration in mitochondria, inhibiting macromolecular biosynthesis and both inhibiting and stimulating certain enzymes. Other important properties of these compounds are discussed including their anti-angiogenic, MDR-revertant and antioxidant properties. It is hoped that this eulogy of the importance of the dienone group will encourage researchers to consider incorporating this structural unit into candidate cytotoxins in the future.

Cytotoxic and Topographical Properties of 6-Arylidene-2-dimethylaminomethylcyclohexanone Hydrochlorides and Related Compounds

A number of 2-arylidenecyclohexanones (1a-h) were converted into the corresponding Mannich bases (2a-h) and (3a,f). Evaluation against murine L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes revealed the marked cytotoxicity of the Mannich bases and also the fact that almost invariably these compounds were more potent than the precursor enones (1a-h). Further evaluation of most of the Mannich bases towards a panel of nearly 60 human tumour cell lines confirmed their utility as potent cytotoxins. In this assay, the compounds showed growth-inhibiting properties greater than the anticancer alkylator melphalan. QSAR studies revealed that in some cell lines compounds possessing small electron-attracting aryl substituents showed the greatest potencies. Molecular modeling and X-ray crystallography demonstrated that various interatomic distances and torsion angles correlated with cytotoxicity. A representative compound (2a) demonstrated weak inhibiting properties towards human N-myristoyltransferase and stimulated a tyrosine protein kinase. A single dose of 100 mg/kg of most of the compounds did not prove to be lethal in mice.

Design, synthesis and antiproliferative activity of some 3-benzylidene-2,3-dihydro-1-benzopyran-4-ones which display selective toxicity for malignant cells

A series of 3-benzylidene-4-chromanones 1a-l were prepared and their cytotoxicity towards human Molt 4/C8 and CEM T-lymphocytes as well as murine L1210 lymphoid leukemia cells were compared to the previously generated biodata in these three assays for the isosteric 2-benzylidene-1-tetralones 2a-l. Over 40% of the compounds in series 1 were more potent than their counterparts in series 2, while equipotency was noted in one-third of the comparisons made. In general the IC(50) values of 1a-l towards the human T-lymphocytes were in the low micromolar range. Molecular modelling revealed differences in shapes of representative molecules in series 1 and 2 which may contribute to the variation in cytotoxic potencies. Most of the compounds in series 1 displayed greater potencies towards HSC-2, HSC-3, HSC-4 and HL-60 neoplasms than HGF, HPC, and HPLF normal cells and were well tolerated in mice.

CoMFA and CoMSIA studies on 1,3-bis(benzylidene)-3,4-dihydro-1H-naphthalen-2-one, 2,6-bis(benzylidene)cyclohexanone, and 3,5-bis(benzylidene)-4-piperidone series of cytotoxic compounds

A number of 1,3-bis(benzylidene)-3,4-dihydro-1H-naphthalen-2-ones, 2,6-bis(benzylidene)cyclohexanones, and 3,5-bis(benzylidene)-4-piperidones possess significant potencies toward L1210, Molt 4/C8, and CEM cell lines. The objective of the current 3D QSAR study is to discover some of the structural parameters which govern cytotoxic potencies. The CoMFA models with steric and electrostatic fields provided satisfactory statistical data [(r2cv = 0.485, r2ncv = 0.834, r2pred = 0.591), (r2cv = 0.532, r2ncv = 0.850, r2pred = 0.729), and (r2cv = 0.561, r2ncv = 0.864, r2pred = 0.666)] in regard to the cytotoxic potencies observed toward L1210, Molt 4/C8, and CEM cell lines, respectively. The CoMSIA model with steric, electrostatic, hydrophobic, and H-bond donor fields exhibited r2cv = 0.513, r2ncv = 0.833, and r2pred = 0.562 for cytotoxic activity toward L1210 cells, while the best CoMSIA models were obtained by a combination of steric, electrostatic, and hydrophobic fields which yielded statistically significant data [(r2cv = 0.531, r2ncv = 0.828, r2pred = 0.652) and (r2cv = 0.560, r2ncv = 0.841, r2pred = 0.729)] to explain the cytotoxicity toward Molt 4/C8 and CEM cells, respectively. The information obtained from the CoMFA and CoMSIA 3D contour maps can be used in the design of more potent cytotoxins.

Cytotoxic 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienes mounted on alicyclic scaffolds

The 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienyl pharmacophore was incorporated into four series of compounds 1-4. Compounds 1a-g comprised a cluster of 3-arylidene-1-(4-nitrophenylmethylene)-2-oxo-3,4-dihydro-1H-naphthalenes while the analogues 2a-g consisted of a group of 6-arylidene-2-(4-nitrophenylmethylene)cyclohexanones. Three other compounds prepared in this study were 1-(4-nitrophenylmethylene)-3-(3,4,5-trimethoxyphenylmethylene)-2-oxo-2,3-dihydro-1H-indene 3a as well as two 5-arylidene-2-(4-nitrophenylmethylene)cyclopentanones 4a,b. The compounds were evaluated against human Molt 4/C8 and CEM T-lymphocytes as well as murine L1210 cells. In general, the compounds in series 1 displayed marked cytotoxicity having IC50 values in the 1-5 microM range while the related cyclohexyl analogues in series 2 were slightly less potent (IC50 figures were mainly 5-10 microM). The relative locations of two aryl rings present in all four series were considered to contribute significantly to bioactivity and may have accounted for the virtual absence of cytotoxic properties in series 3 and 4. Most of the compounds were administered intraperitoneally to mice using doses up to and including 300 mg/kg. No mortalities were noted. The inhibiting effect of most of the compounds towards Helicobacter pylori is noteworthy. The modes of action of representative compounds include the induction of apoptosis while some compounds weakly inhibited tubulin polymerisation and human N-myristoyltransferase.

Modelling steric effects in DNA-binding platinum(II)-am(m)ine complexes

A repulsive energy strategy has been employed in an attempt to delineate the steric contribution to the biological profile of a variety of platinum-am(m)ine complexes. Thus, relative steric descriptors have been calculated for the amine ligands themselves by the Ligand Repulsive Energy (LRE) methodology. This has been extended to a Complex Repulsive Energy (CRE) strategy whereby the steric requirements of the approach of a metal complex to a site on a target molecule may be evaluated. Specifically, the monodentate approach of a variety of platinum-am(m)ine complexes to the N7 site of a guanine moiety has been considered. The steric descriptors thus obtained have been used in QSAR analysis, resulting in improved regression equations. Attempts have also been made to relate the above descriptors to various biological indicators for given series of complexes. These investigations suggest an optimum steric requirement for minimum toxicity, which could aid in the rational design of such agents.