Synthesis and anticancer activities of 4-oxobenzopyrano[2,3-d]pyrimidines

Several 2-aryl-4-oxoxbenzopyrano[2,3-d]pyrimidines have previously been shown to exhibit in vivo antitumor activity in mice with P388 lymphocytic leukemia. In the present study, a series of novel substituted benzopyrano[2,3-d]pyrimidines have been prepared and tested for cytotoxic activity against a panel of cancer cell lines including the P388 lymphocytic leukemia cell line. The unsubstituted parent compound, some methoxylated derivatives and a cyclohexyl derivative all exhibited potent cytotoxic activity (IC50 values 0.3-0.64 microM). A number of derivatives, including the unsubstituted parent pyrimidine, were shown to cause a significant perturbation in cell cycle kinetics with an observed 2- to 3-fold increase in cells in the G2/M phase of the cell cycle. Furthermore, a polymethoxylated derivative, 2-(3,4,5-trimethoxyphenyl)-9-methoxy-4-oxo-2,3-dihydrobenzopyrano[ 2,3-d]pyrimidine 13, was shown to be selectively active against a number of human ovarian cell lines.

Positron emission tomography of murine liver metastases and the effects of treatment by combretastatin A-4

There are major potential advantages in non-invasive measurement of preclinical tumour biology and therapeutic response in clinically relevant, internal body sites, notably the ability to follow outcome in individual animals rather than averaging results from groups. We have exploited positron emission tomography (PET) to determine the feasibility of detecting liver metastases in B6D2F1 mice using fluorine-18 fluorodeoxyglucose ([18F]FDG) both before and after treatment by the novel cytotoxic agent, combretastatin A-4. The normal distribution of [18F]FDG in the absence of disease was characterised, with the clear delineation of the brain, the heart and the urinary bladder in all studies. In untreated mice with liver metastases, a strong correlation (r2 = 0.98) was found between the quantitative estimates of [18F]FDG uptake obtained by analysis of PET images, and those obtained from ex vivo assay of liver plus metastases excised immediately after imaging. In this first series, the effective limit of resolution was in livers containing a number of small metastases (range 8-14) with a single volume equivalent of approximately 200 mm3. PET image analysis was concordant with histological measurements in showing that single intraperitoneal doses of combretastatin A-4 resulted in an average 30% volume destruction of metastatic mass by 24 h following administration.

Tubulin as a target for anticancer drugs: agents which interact with the mitotic spindle

Tubulin is the biochemical target for several clinically used anticancer drugs, including paclitaxel and the vinca alkaloids vincristine and vinblastine. This review describes both the natural and synthetic agents which are known to interact with tubulin. Syntheses of the more complex agents are referenced and the potential clinical use of the compounds is discussed. This review describes the biochemistry of tubulin, microtubules, and the mitotic spindle. The agents are discussed in relation to the type of binding site on the protein with which they interact. These are the colchicine, vinca alkaloid, rhizoxin/maytansine, and tubulin sulfhydryl binding sites. Also included are the agents which either bind at other sites or unknown sites on tubulin. The literature is reviewed up to October 1997.

Antimitotic activity of diaryl compounds with structural features resembling combretastatin A-4

Series of diaryl ethers, amines and amides have been synthesized and tested for antitumor activity. These diaryl compounds possess some of the structural features of combretastatin A-4 (a potent antimitotic agent). They were designed to discover whether transferring these structural motifs from stilbenes to heterosubstituted diaryl compounds would enhance their biochemical activities. Molecular modeling studies suggested that these diaryl compounds could adopt conformations similar to combretastatin A-4. However, although some agents (5-7) were cytotoxic and others (10 and 12) could interact with tubulin, none were as potent as combretastatin A-4.

Potent antimitotic and cell growth inhibitory properties of substituted chalcones

A series of substituted chalcones was synthesised and screened for cytotoxic activity against the K562 human leukaemia cell line. (E)-3-(3"-Hydroxy-4"-methoxyphenyl)-2-methyl-1-(3',4',5'- trimethoxyphenyl)-prop-2-en-1-one [IC50 (K562) 0.21 nM] was found to be the most active. A relationship between the conformation and cytotoxicity of the chalcones is discussed.

Molecular modeling of the interaction of anthracenyl-amino acid topoisomerase inhibitors with the DNA sequence d(CGTACG)

Anthracenyl-amino acid and dipeptide conjugates represent new classes of topoisomerase (topo) inhibitors. To investigate the structural basis for their different selectivity against topo I and II and varying potency, the binding of six compounds to d(CGTACG) was studied by molecular modeling. Modeling data were in good agreement with physical data showing that five compounds intercalated DNA with the anthraquinone chromophore orientated in parallel to the long dimension of the d(CpG) base pairs and the amino acid placed in the minor groove. Differences in binding modes emerged which correlated to different biological properties. The amino acid chain of the topo I inhibitor (NU/ICRF 600, gly-phe) extended significantly out from the helical axis horizontal. The amino acid side chains of two topo II inhibitors (NU/ICRF 510, arginine and NU/ ICRF 512, methionine) were inserted into the minor groove, whereas the C-terminal groups (hydrazide) of two potent topo II inhibitors (NU/ICRF 500 and 506, serine) were placed into the minor groove while the amino acid side chains pointed away from the minor groove. These data provide structural information which may prove valuable in rational design of second generation analogs.

Isolation of aurantiamide acetate from Arisaema erubescens

Aurantiamide acetate (N-benzoyl-1-phenylalanyl-1-pheylalaninol acetate) has been isolated by chromatographic separation of a methanol extract of Arisaema erubescens and its structure confirmed by synthesis.

Biochemistry of topoisomerase I and II inhibition by anthracenyl-amino acid conjugates

Mono-conjugation of an anthraquinone nucleus with a range of naturally occurring amino acids chemically modified at their C-terminus has been adopted as a synthetic approach in the rational design of novel topoisomerase (topo) inhibitors. The biochemistry of topo I and II inhibition has been investigated for a series of 16 new compounds (NU/ICRF 500-515) from which structure-activity relationships have been investigated. Only three compounds could be demonstrated to bind to DNA: two serine derivatives (NU/ICRFs 500 and 506) and an arginine derivative (NU/ICRF 510). In decatenation and relaxation assays with purified enzyme, several compounds were shown to be potent catalytic inhibitors of topo II (100% inhibition at 5 micrograms/mL (10-15 microM) or less) without stabilizing cleavable complex formation. These included the three DNA binding species (of which NU/ICRF 506 was the most active) and a dihydroxyphenylalanine analogue (NU/ICRF 513). Both NU/ICRFs 500 and 506 were further shown to antagonize DNA cleavage induced by amsacrine. Only NU/ICRF 506 unequivocally inhibited the catalytic activity of topo I without induction of DNA cleavage, and was the only combined topo I and II catalytic inhibitor. One compound, NU/ICRF 505 (tyrosine conjugate), stabilized topo I cleavable complexes without inhibiting the catalytic activity of topo I and II. Modifications to the structure of NU/ICRF 505 revealed that the presence of an unhindered hydroxyl on the tyrosine ring and a more hydrophobic ethyl ester at the amino acid C-terminal were both essential, suggesting a highly specific interaction between drug, enzyme and DNA in the ternary complex. Molecular modelling studies suggested that the observed differences in topo inhibition are a consequence of major conformational alterations brought about by small changes in the amino acid substituent, and confirmed a rigid structural requirement for the induction of topo I cleavage, in addition to a less rigid structural requirement for topo II inhibition. A strong correlation was observed between topo inhibition and in vitro cytotoxicity against the human ovarian cancer cell line A2780 (IC50 range 3.4-11.6 microM), suggesting a mechanism of cell kill, at least in part, involving topo inhibition.

The interaction with tubulin of a series of stilbenes based on combretastatin A-4

A series of stilbenes, based on combretastatin A-4, were synthesised. A structure-activity study was carried out to characterise the interaction of these agents with tubulin. The substitution of small alkyl substituents for the 4'-methoxy group of combretastatin A-4 and the loss of the 3'-hydroxyl group does not have a major effect on the interaction with tubulin. trans-Stilbenes were shown to bind tubulin, but do not inhibit microtubule assembly. This work, together with previous studies, has been used to propose an idealised structure for a tubulin-binding agent of this type.

Structure-activity studies on 2-aryl-4H-3,1-benzoxazin-4-ones

Eight benzoxazin-4-ones related in structure to NSC 341964 (1) have been tested for cytotoxicity in two different cell systems. Two of the benzoxazin-4-ones (3 and 10) showed good cytotoxicity (ID50 = 9.9 and 8.9 microM) in P388 cells. The nitrobenzoxazin-4-one (10) caused a significant alteration in cell cycle distribution when administered to P388 cells and was an inhibitor of porcine pancreatic elastase. Structure-activity relationships are discussed.

Bioactivity and molecular modelling of diphenylsulfides and diphenylselenides

Bis(2-bromo-4,5-dimethoxyphenyl)sulfide (5) and bis(2-bromo-4,5-dimethoxyphenyl) selenide (7) have been shown to block cells in the G2/M phase of the cell cycle, whereas the debromo (4,6) equivalents do not. The biobromoselenide (7) is cytotoxic to tumour cells in vitro and has been shown to increase the mitotic index of treated cells. These biological effects are consistent with disruption of the mitotic apparatus. This agent does not inhibit microtubule assembly in vitro, but does bind to tubulin. Molecular modelling of these structures indicates that their spatial and electronic structures may make an important contribution to the biological activity.

The suitability of carboplatin solutions for 14-day continuous infusion by ambulatory pump: an HPLC-dynamic FAB study

The stability of aqueous carboplatin solutions over 14 days has been studied at 37 and 60 degrees C. High-performance liquid chromatography and dynamic FAB mass spectrometry studies have shown that carboplatin solutions were stable at 37 degrees C but degraded at 60 degrees C. Fluid loss through evaporation was significant at the higher temperature.

Dimethanesulphonate esters in receptor mapping studies. 2. Antitumour activities of alkyl and alkoxy dimethanesulphonates substituted on a benzene nucleus

The antitumour activities of 15 novel aromatic dimethanesulphonate esters were studied. Several alkyl and alkoxy compounds have shown good antitumour activity whilst similar isomers have proved ineffective as antitumour agents. These differences in activity have been correlated with the length of the sidechain substituents and their relative flexibilities.

Dimethanesulphonate esters in receptor mapping studies. 1. Benzene 1,2-, 1,3- and 1,4-diol, dimethanol and diethanol dimethanesulphonates and anti-tumour activity

The anti-tumour activities of nine aromatic dimethanesulphonate esters were examined. Their biological effects have been related to both their chemical reactivity and to the computer-modelled vectorial positions of the centres of alkylation of the compounds. One compound (19) has shown activity between sensitive and resistant Yoshida tumours in vivo and also shows the highest activity between these two cell lines in vitro. In its minimal energy form, this compound would require to interact with converging nucleophilic centres about 6 A apart, and it is tentatively suggested that this may be an appropriate dimension for a receptor which is required to be alkylated in order to show anti-tumour activity.

The effect of ifosfamide and its metabolites on intracellular glutathione levels in vitro and in vivo

The effect of ifosfamide and its metabolites on intracellular levels of glutathione in P388 cells in vitro has been studied. It is demonstrated that glutathione depletion occurs only in the presence of 4-hydroperoxyifosfamide and chloroacetaldehyde. In contrast isophosphoramide mustard had no effect on glutathione levels in intact cells. The concentration of 4-hydroperoxyifosfamide required to reduce glutathione levels by 50% was approximately 1 mM and this represents a concentration far in excess of that achievable in patients receiving the drug. However the concentration of chloroacetaldehyde (approximately 100 microM) required to reduce intracellular levels of glutathione to a similar extent is attained in patients receiving ifosfamide. The glutathione levels in lymphocytes isolated from a patient undergoing an eight hour infusion of ifosfamide showed a marked decrease to about 30% of their original value. We conclude that ifosfamide causes glutathione depletion in vivo and the majority of this can be accounted for by the production of chloroacetaldehyde.