Ability of Group IVB metallocene polyethers containing dienestrol to arrest the growth of selected cancer cell lines

BACKGROUND

Monomeric Group IVB (Ti, Zr and Hf) metallocenes represent a new class of antitumor compounds. There is literature on the general biological activities of some organotin compounds. Unfortunately, there is little information with respect to the molecular level activity of these organotin compounds. We recently started focusing on the anti-cancer activity of organotin polymers that we had made for other purposes and as part of our platinum anti-cancer effort.

METHODS

For this study, we synthesized a new series of metallocene-containing compounds coupling the metallocene unit with dienestrol, a synthetic, nonsteroidal estrogen. This is part of our effort to couple known moieties that offer antitumor activity with biologically active units hoping to increase the biological activity of the combination. The materials were confirmed to be polymeric using light scattering photometry and the structural repeat unit was verified employing matrix assisted laser desorption ionization mass spectrometry and infrared spectroscopy results.

RESULTS

The polymers demonstrated the ability to suppress the growth of a series of tumor cell lines originating from breast, colon, prostrate, and lung cancers at concentrations generally lower than those required for inhibition of cell growth by the commonly used antitumor drug cisplatin.

CONCLUSION

These drugs show great promise in vitro against a number of cancer cell lines and due to their polymeric nature will most likely be less toxic than currently used metal-containing drugs such as cisplatin. These drugs also offer several addition positive aspects. First, the reactants are commercially available so that additional synthetic steps are not needed. Second, synthesis of the polymer is rapid, occurring within about 15 seconds. Third, the interfacial synthetic system is already industrially employed in the synthesis of aromatic nylons and polycarbonates. Thus, the ability to synthesize large amounts of the drugs is straight forward.

Synthesis of the catechols of natural and synthetic estrogens by using 2-iodoxybenzoic acid (IBX) as the oxidizing agent

A method for the synthesis of 2-hydroxyestrone/estradiol, 4-hydroxyestrone/estradiol, 3'-hydroxydiethylstilbestrol, 3'-hydroxyhexestrol, and 3'-hydroxydienestrol is reported, in which 2-iodoxybenzoic acid (IBX) and the corresponding phenolic estrogen are reacted. Treatment of the natural estrogens, estrone/estradiol, with stoichiometric amounts of IBX in dimethylformamide initially yielded a mixture of estrone/estradiol-2,3- and -3,4-quinones, which were reduced in situ to the corresponding catechols by treatment with a 1 M aqueous solution of ascorbic acid. Chromatographic separation of the reaction products afforded 2- and 4-hydroxyestrone/estradiol in good overall yields (79%). In the case of the synthetic estrogens containing two identical phenolic rings, protection of one ring is a prerequisite for the synthesis of the monocatechol. Thus, diethylstilbestrol and dienestrol were protected at one phenol ring as their methyl ethers. The resulting monophenols were treated with stoichiometric amounts of IBX for 1 h, followed by treatment with 1 M aqueous ascorbic acid to obtain the corresponding catechols in more than 70% yield. Furthermore, the catechol of diethylstilbestrol, protected at one ring, was reduced by catalytic hydrogenation at the C3-C4 double bond to obtain 3'-hydroxyhexestrol in 90% yield. Removal of the protected methoxy groups of the synthetic estrogen catechols was carried out by treatment with a 1 M solution of boron tribromide in dichloromethane. This method is highly efficient for the preparative scale synthesis of catechols of both natural and synthetic estrogens.

Promotive effects of diethylstilbestrol, its metabolite (Z,Z-dienestrol) and a stereoisomer of the metabolite (E,E-dienestrol) in tumorigenesis of rat mammary glands pregnancy-dependently initiated with radiation

Wistar-MS rats received whole body irradiation with 260 cGy gamma-rays at day 20 of pregnancy and then were treated with diethylstilbestrol (DES), E,E-dienestrol (E,E-DIES) or Z,Z-dienestrol (Z,Z-DIES) for 1 year. DES administration caused the highest incidence of mammary tumors with a concomitant reduction of gain in body weight. When E,E-DIES or Z,Z-DIES in pellet form was implanted, the incidence of tumors was significantly lower than that observed in rats treated with DES. To clarify the increased susceptibility to mammary tumorigenesis after DES administration we measured hormone levels in the serum of rats implanted with pellets containing derivatives of the synthetic estrogens. The serum prolactin concentration was significantly increased by DES administration. When E,E-DIES or Z,Z-DIES pellets were implanted the prolactin level was markedly reduced to 4.5% and 0.7% of that observed in DES-treated rats, respectively. In addition, the serum concentrations of estradiol-17 beta and progesterone in rats with Z,Z-DIES pellets were higher than those of rats with DES or E,E-DIES pellets. A large number of DES-induced mammary tumors were positive for both estrogen and progesterone receptors, but no tumors negative for both receptors were obtained. The findings suggest that DES acts directly on radiation-initiated mammary cells via binding with estrogen receptors and/or stimulates the secretion of prolactin from the pituitary glands.

Formation of free radicals and active oxygen species from diethylstilbestrol and its derivatives

Diethylstilbestrol (DES), an estrogen analogue, was converted into a free radical in alkaline dimethyl sulfoxide as well as in an H2O2/peroxidase system. The presence of the hydroxyl group of the DES molecule was essential to free radical formation. Indenestrol A (IA), a microsomal metabolite of DES, showed a paramagnetic property without enzymatic activation. The electron spin resonance spectrum of IA seemingly corresponded to that of the enzymatically formed DES radical. In an NADH/peroxidase system, DES induced concomitant production of active oxygen species, which were also produced by IA. Related compounds of IA were also examined to compare with DES and IA. The significance of the free radical is discussed in relation to the process of carcinogenesis by DES.