Carrier mediated action of platinum complexes on estrogen receptor positive tumors

Synthesis of 17β-estradiol-linked platinum(II) complexes and their cytocidal activity on estrogen-dependent and -independent breast tumor cells

The synthesis of two new highly potent 17beta-estradiol-linked platinum(II) complexes is described. The new molecules are linked at position 16 of the steroid nucleus with an alkyl chain. They are made from estrone in nine chemical steps with an overall yield exceeding 10%. The biological activity of these compounds was evaluated in vitro on estrogen dependent and independent (ER(+) and ER(-)) human breast tumor cell lines: MCF-7 and MDA-MB-231. The novel compounds prove to be highly cytotoxic against breast cancer cell lines. The most cytotoxic derivative shows high affinity for the estrogen receptor alpha.

Reduction of the estrogenic side effects of the mammary tumor-inhibiting drug [1,2-bis(2,6-dichloro-4-hydroxyphenyl)- ethylenediamine]dichloroplatinum(II) by variation of ring substituents

[1,2-Bis(4-methoxy/4-hydroxyphenyl)ethylenediamine]dichloroplatinum-(II) complexes with Cl-, CH3-, or OCH3-substituents in the ortho-positions of the aromatic rings (meso-1-PtCl2, D,L-1-PtCl2, meso-2-PtCl2, D,L-2-PtCl2, meso-3-PtCl2, meso-4-PtCl2, meso-5-PtCl2) were tested on the MDA-MB 231 breast cancer cell line, the lymphocytic leukemia P388, and the estrogen receptor-positive and -negative MXT mammary carcinoma of the mouse (MXT,ER(+)-MC, MXT,ER(-)-MC). The comparison of the effects of methoxy-substituted complexes (meso-1-PtCl2, D,L-1-PtCl2, meso-3-PtCl2) with those of the respective hydroxy-substituted ones (meso-2-PtCl2, D,L-2-PtCl2, meso-4-PtCl2) shows that a reduction of estrogenic effects as well as a total loss of the mammary tumor-inhibiting activity takes place on methylation of the 4-OH group. The exchange of the 2,6-standing chlorine atoms by methyl groups in meso-2-PtCl2 led to the non-estrogenic, but on the MXT,ER(+)-MC highly effective derivative meso-4-PtCl2 which proved to be also cytotoxic on ER(-)-tumors such as MXT,ER(-)-MC, and the P388 leukemia.

The effect of a combination of zindoxifene and cisplatin on Dunning R3327-G prostatic carcinomas of the rat

Endocrine therapy of hormone-dependent prostatic carcinomas can be very effective at the beginning. However, tumour growth eventually resumes possibly because of the presence of androgen-independent cell clones. Addition of a cytotoxic agent to the hormonally active drug at an early stage could possibly delay progression of disease. Therefore, we studied the effects of hormonal and cytostatic treatment in a rat prostate carcinoma model: freshly transplanted Dunning R3327-G prostatic tumours of the rat were treated with the partial antioestrogen zindoxifene and cisplatin alone and in combination. In addition we tested a 2-phenylindole-linked platinum complex 3-PtCl2, which contains both effective functions. This particular complex had only a weak non-significant inhibitory effect on tumour growth. Comparing monotherapies with zindoxifene or cisplatin at various dose levels with the corresponding combinations, it became evident that the latter treatment was significantly more effective than the use of single agents. A very low dose of 0.4 mg cisplatin together with 2 mg/kg zindoxifene inhibited tumours by 91%, which was close to the effects of castration or diethylstilbestrol (1 mg). The analyses of accessory sex organs revealed much weaker oestrogenic side-effects than those observed with diethylstilbestrol at an equivalent dose. These results demonstrated that it is possible to increase the efficacy of hormonal therapy of prostatic carcinomas by concomitant administration of cisplatin and reduce side-effects of oestrogenic drugs.

Dunning R3327-G prostate carcinoma of the rat: an appropriate model for drug evaluation

Models for testing new drugs for the treatment of hormone-dependent prostate cancer are restricted to a few in vivo rat tumour lines; most of them originating from the Dunning R3327 adenocarcinoma. The original tumour and the R3327-H line grow rather slowly leading to a long duration of therapeutic experiments. The R3327-G subline can be transplanted as a cell suspension or tumour fragments, which give rise to fast and rather homogeneously growing androgen-dependent tumours. Their growth is strongly inhibited by castration or administration of diethylstilbestrol. Experiments were terminated 5 weeks after transplantation. Best results were obtained when treatment was started 1 day after transplantation. Histological sections showed therapy-dependent changes in the microarchitecture of these prostate tumours. The direct inhibitory effect of antiandrogens on prostate tumours was demonstrated when castrated, testosterone-propionate-supplemented animals were used. The short duration of experiments and reproducible responses to standard therapies are the advantages of this tumour model.