John A. Hadfield

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.

Structural requirements for the interaction of combretastatins with tubulin: how important is the trimethoxy unit?

A series of combretastatins possessing both a trimethoxy unit and other substituents on ring A has been synthesised and tested for cytotoxicity and their ability to interact with the protein tubulin. All previous studies have indicated that the trimethoxy unit is essential for interaction with tubulin. The studies herein show that molecules possessing functionalities other than trimethoxy can also interact with tubulin. Importantly a trimethyl substituted agent 52a has shown reduced cytotoxicity, but increased potency in its ability to inhibit the assembly of tubulin.

Isoflavones inhibit intestinal epithelial cell proliferation and induce apoptosis in vitro

SummaryThere have been many reports that high soya-based diets reduce the risk of certain types of cancer. This effect may be due to the presence of high levels of isoflavones derived from the soya bean, particularly genistein which has been shown to be a protein tyrosine kinase (PTK) inhibitor and have both oestrogenic and anti-oestrogenic properties. We have examined the effect of genistein and a number of novel synthetic analogues on both normal (IEC6, IEC18) and transformed (SW620, HT29) intestinal epithelial cell lines. Responses were compared to those elicited by oestradiol, the anti-oestrogen tamoxifen, and the tyrosine kinase inhibitor tyrphostin. Genistein and tamoxifen were potent inhibitors of cell proliferation. Of seven novel isoflavones tested, none were more potent inhibitors than genistein, and all displayed similar relative activities across the different cell lines. In addition to inhibiting cell proliferation, cell death via apoptosis was observed when the cells were exposed to the isoflavones and all but one exhibited PTK inhibitory activity. These data suggest that by reducing proliferation and inducing apoptosis, possibly due in part to PTK inhibition, isoflavones may have a role in protecting normal intestinal epithelium from tumour development (reducing the risk) and may reduce colonic tumour growth.

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.

Cytotoxic Michael-type amine adducts of α-methylene lactones alantolactone and isoalantolactone

Two series of cytotoxic (IC50, K562 cell line, 1–24 μM) α-aminomethyl substituted lactones 3 and 4 were prepared by stereoselective Michael-type addition of amines to alantolactone (1) and isoalantolactone (2). The lactones 1 and 2 and their amine adducts induce apoptosis and act as alkylating agents.

Synthesis and anticancer activity of fluorinated analogues of combretastatin A-4

Abstract The synthesis of a series of fluorinated benzaldehydes and their use in the Wittig synthesis of fluoro-substituted stilbenes is described. 3,5-Difluoro-4-hydroxybenzaldehyde (6) and 3-fluoro-4-methoxybenzaldehyde (11) are prepared by Duff formylation of 3,5-difluorophenol and 2-fluoroanisole, respectively. 2-Methoxy-3,4-difluorobenzaldehyde was obtained by Friedel–Crafts formylation of 2,3-difluoroanisole with α,α-dichloromethyl methyl ether. The aldehydes were used to make a series of fluorinated analogues of the anticancer combretastatins A-1, A-2 and A-4. The in vitro anticancer properties of the fluoro combretastatins are reported. The most active fluoro analogue 3-deoxy-3-fluoro-combretastatin A-4 (Z-2) retains the potent cell growth inhibitory properties of CA-4.

Reaction of Baylis-Hillman products with Swern and Dess-Martin oxidants

Abstract The Baylis–Hillman adducts of aryl aldehydes and alkyl acrylates are efficiently oxidized to the corresponding α-methylene-β-keto esters with the Dess–Martin periodinane. The attempted Swern oxidation of the same adducts resulted in S N 2′-type substitution of the allylic hydroxyl group by chloride.

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.

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.

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.