Chemotherapy of Prostatic Cancer. In: Bruce AW, Trachtenberg J, editors. Adenocarcinoma of the Prostate. London: Springer; 1987. pp. 185-96. [DOI: 10.1007/978-1-4471-1398-0_12]

Platinum(II) complexes interfering with testicular steroid biosynthesis: drugs for the therapy of advanced or recurrent prostate cancers? Preclinical studies

[Meso-1,2-bis(2,6-dihalo-3/4-hydroxyphenyl)ethylenediamine]platinum(II) complexes (meso-1-PtLL': 2,6-F(2),3-OH; meso-2-PtLL': 2,6-F(2),4-OH; meso-3-PtLL': 2,6-Cl(2),3-OH; meso-4-PtLL': 2,6-Cl(2),4-OH; L = OH(2), L' = OSO(3) or L,L' = Cl(2)) were designed with the aim to get drugs comprising both cytotoxic and testosterone level lowering potencies. It is assumed that such compounds are more efficient than the established endocrine therapeutic measures and can affect the development of hormone refractory prostate cancer (PC). With exception of meso-3-PtLL' all Pt-complexes and the comparison compound cisplatin significantly reduced the testosterone level in experiments on male rats. However, in the test on the Dunning R3327 PC of the rat only cisplatin and meso-4-PtLL' showed a significant anti-tumor activity at well-tolerated dose ranges. Meso-4-PtLL' also significantly extended the time to disease progression in comparison with orchiectomy in this tumor model. Interestingly, the relapsed tumor, too, responded to meso-4-PtLL' as demonstrated in a long-term study on orchiectomized rats bearing Dunning R3327 PC grafts. This effect cannot be ascribed to cytotoxic effects of meso-4-PtLL' because of its inactivity on the human LNCaP/FGC PC cell line. Therefore, the contribution of an additional mechanism to the anti-prostate cancer activity of meso-4-PtLL', presumably owing to its estrogenic potency, must be considered. This assumption was supported by test results with diethylstilbestrol (DES) (non-steroidal estrogen) on the Dunning R3327 PC of the rat relapsed after orchiectomy. This tumor model was strongly inhibited by DES. The possible mode of action of meso-4-PtLL' is thoroughly discussed.

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.

[1,2-Bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine] dichloro-platinum(II): an endocrine-active platinum complex with a specific prostatic tumor-inhibiting activity

[1,2-Bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine]dichloro-platinum (II), (C), a platinum complex with endocrine activity and a specific effect on hormone-dependent mammary tumors, was tested for its tumor-inhibitory activity in the hormone-sensitive R 3327 and Nb prostate carcinoma models of the rat and for its endocrine activities in comparison to the ligand L and diethylstilbestrol (DES). Established tumors of the R 3327 prostate tumor were strongly inhibited by C. Its effect equaled that of DES and was significantly better than that of L. Accessory sex organ weights and testosterone levels were strongly reduced by C as well as L. This antigonadotrophic effect, which is almost comparable to DES, was confirmed in 10 day experiments with intact, mature mice and rats, whereas a direct antiandrogenic activity was not given. A part of the antitumor action of C is therefore due to this antigonadotrophic activity. Affinities to estrogen, progesterone, and androgen receptors, however, were very low. The hormone-sensitive Noble Nb-R prostatic carcinoma was almost completely inhibited by C, whereas L had only a weak effect. As C has no significant effect on the hormone-independent R 3327 HI prostate tumor and as its effect on hormone-dependent tumors is significantly better than that of the ligand L in spite of their similar endocrine properties, an apparently specific antiproliferative effect of C only on hormone-dependent prostate tumors is obvious. This was further shown in a long-term experiment with the R 3327 prostate carcinoma. Whereas tumors in the castration group relapsed from androgen ablation and exerted a progressive tumor growth, therapy with C almost completely prevented this relapse phenomenon. After 25 weeks of treatment, C inhibited tumor growth by 90% compared to castration. Owing to these results, this new endocrine active platinum complex with an apparently specific effect on hormone-dependent prostate tumors can be of value for the therapy of the prostatic carcinoma.