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

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.

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.

Investigation of the conformational influences on the estrogenic activity of 1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines and of their platinum(II) complexes, II: Synthesis and studies on the estrogenic activity of cis- and trans[bis(2,6-dichloro-4-hydroxybenzylamine)]dihaloplatinum(II)-c omplexes

2,6-Dichloro-4-hydroxybenzylamine (1) and its N-methyl (2) and N-ethyl (3) derivatives were synthesized and tested for estrogen receptor affinity as well as for estrogenic activity. In contrast to their related highly active 1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamines (meso-4 - meso-6) none of the benzylamines showed hormonal activity. The coordination of the benzylamine 1 to platinum did not lead to an estrogenic compound. The reasons for the different activity of [meso- 1,2(bis-2,6-dichloro-4-hydroxyphenyl)ethylenediamine]dichloroplatinum(II ) (meso-4-PtCl2) and cis[bis(2,6-dichloro-4-hydroxybenzylamine)]dichloroplatinum(II) (cis-1-PtCl2), the latter of which can be considered as a ring-opened counterpart of the highly active meso-4-PtCl2, are thoroughly discussed under inclusion of conformational facts. The results of this and the preceding work show, that the pharmacophore meso-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine (meso-4) which is exclusively responsible for the estrogenic activity of meso-4-PtCl2 causes comparable hormonal effects in two different conformations with O-O distances of about 8 A (complex) and of about 12 A (diamine). Therefore, we discuss two binding sites for estrogens in their receptor.

Aqua[1-(2,6-dichloro-4-hydroxyphenyl)-2- phenylethylenediamine]sulfatoplatinum(II) complexes with variable substituents in the 2-phenyl ring, II: Correlation of molecular structure and estrogenic activity of breast and prostate cancer inhibiting. [erythro-1-(2,6-dichloro-4-hydroxyphenyl)-2-(2-halo-4- hydroxyphenyl)ethylenediamine]platinum(II) complexes

Complete three-dimensional X-ray crystal structure analyses of estrogenic [erythro-1-(2,6-dichloro-4-hydroxyphenyl)-2-(2-halo-4- hydroxyphenyl)ethylenediamine]diiodoplatinum(II) complexes (halo = fluoro:erythro-8PtI2 and halo = chloro:erythro-9-PtI2) which were synthesized for application in breast and prostate cancer, have been carried out. 6239 as well as 6521 reflexes were measured and refined to an R-value of 0.105 and 0.066, respectively. The molecules of erythro-8-PtI2 are displaced laterally from a possible Pt-Pt-axis separated, alternatingly, by Pt-Pt-distances of 3.62 A and 6.27 A. A comparable structure possesses erythro-9-PtI2 with Pt-Pt-distances of 3.59 A and 6.32 A. The ethylenediamine ligands of erythro-8-PtI2 and erythro-9-PtI2 are puckered and exist in half chair conformations. For both complexes the 2,6-dichloro-4-hydroxyphenyl ring is equatorially arranged, while the 2-halo-4-hydroxyphenyl ring is nearly perpendicular to the N-Pt-N plane. The O-O-distance between the phenolic oxygens amounts to 8.1 A in erythro-8-PtI2 and to 7.8 A in erythro-9-PtI2. Though these O-O-distances differ strongly from that (12.1 A), which is considered to be necessary for the binding of an estrogen to its receptor, [1-(2,6-dichloro-4-hydroxyphenyl)- 2-(2-halo-4-hydroxyphenyl)ethylenediamine)]platinum(II) complexes show estrogenic effects which are, however, strongly reduced compared to that of therapeutically used estrogens like diethylstilbestrol. The relationship between molecular structure and estrogenicity as well as the significance of the latter for antitumor activity and untoward side effects are thoroughly discussed.

[meso-1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine]- dichloroplatinum(II), a new drug not only parenterally but also orally active in the therapy of breast and prostate cancer

The platinum complex [meso-1,2-bis(2,6-dichloro-4-hydroxyphenyl)- ethylenediamine]dichloroplatinum(II),K, was tested for its antitumor activity on hormone-sensitive tumor models under peroral administration. The resorption from the gastrointestinal tract was proved by determining the estrogenic effect of K in a dose/activity study using the immature-mouse uterine weight test. In comparison to the subcutaneous injection, a tenfold peroral dose was administered to achieve identical effects. By peroral treatment of the hormone-sensitive MXT(M3.2) mammary carcinoma of the mouse with K an almost complete inhibition of the tumor growth was obtained. This effect was superior to that of subcutaneously applied cisplatin and significantly better than that obtained by perorally administered ligand L at an equimolar dose, indicating that the antitumor effect is caused by the intact complex K and not by the liberated ligand L. The strong antitumor activity of perorally applied K was also demonstrated on the hormone-sensitive Noble Nb-R prostatic carcinoma of the rat. Histological examinations showed that the platinum complex K did not cause cisplatin-like kidney damage or irritations of gastric or intestinal mucosa when given perorally.

Antiproliferative activity of casodex (ICI 176.334) in hormone-dependent tumours

The nonsteroidal antiandrogen casodex has been described as a peripherally selective drug for the treatment of prostatic cancer. In this study we determined its activity in various models of hormone-dependent malignancies including those of the prostate and the breast. Analysis of endocrine effects in rats after 15 days of treatment revealed a strong reduction of the weights of prostates and seminal vesicles and a significant rise of testosterone serum levels as a result of the interference with central feedback mechanisms. The growth of androgen-sensitive human LNCaP/FGC prostate cancer cells was strongly inhibited by casodex. Unlike hydroxyflutamide, casodex was also active in hormone-depleted medium. The inhibitory effect was overcome by addition of testosterone propionate, which indicates an androgen-receptor-mediated mode of action. In rats bearing Dunning R3327-G prostate carcinomas casodex exerted a strong antitumour effect at the beginning of therapy. However, after 4 weeks of treatment tumours resumed growth whereas diethylstilboestrol-treated tumours remained static. In MXT-M3.2 mouse mammary tumours with significant quantities of androgen receptors casodex was also effective in inhibiting tumour growth. After 6 weeks of treatment, tumour weights were reduced by 69% whereas uterine weights were significantly increased, possibly because of a progestin-like activity of the drug. Csodex is very active in various models of hormone-dependent carcinomas. However, the limited duration of action in prostatic tumours and the incomplete growth inhibition in mammary tumours suggest that it should be used only combination with other endocrine therapies.

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.

Chemosensitivity of human MCF-7 breast cancer cells to diastereoisomeric diaqua(1,2-diphenylethylenediamine) platinum(II) sulfates and specific platinum accumulation

Cisplatin, raceme-diaqua[1,2-bis(4-fluorophenyl)ethylenediamine]platinu m(II) sulfate (compound I), meso-diaqua[1,2-bis(4-fluorophenyl)ethylenediamine]-platinum(II) sulfate (compound II), and meso-diaqua[1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]platinum(II) sulfate (compound III) were compared with regard to their effect on the MCF-7 breast cancer cell line in vitro. At equimolar concentrations (5 microM), cisplatin, compound I, and compound II were equiactive after 231 h drug exposure, whereas compound III was ineffective. Although compounds I and II showed markedly greater inactivation than did cisplatin after 6 h incubation with culture medium, compound I (but not compound II) exhibited antitumor activity equivalent to that of cisplatin when cells were exposed to the drugs for 6 h. Platinum measurements by neutron-activation analysis revealed that compound I was selectively and rapidly accumulated by MCF-7 cells, resulting in a high degree of DNA platination within the first few hours of drug exposure. However, when the drug-exposure period was long enough, platinum enrichment was not reflected in an overall difference in the cytotoxicity of compound I vs cisplatin. Nevertheless, compound I should be superior to cisplatin in vivo, provided that effective plasma levels can be maintained for about 6 h.

Effect of zindoxifene on experimental prostatic tumours of the rat

The anti-oestrogen zindoxifene was originally developed as a drug for the treatment of hormone-dependent mammary carcinomas. Experiments with rats bearing androgen-dependent prostatic tumours revealed anti-neoplastic activity of zindoxifene on these tumours also. Therefore, the inhibitory effect of this drug was studied in various prostatic tumour models in comparison to the anti-oestrogen tamoxifen and to castration. The growth of the hormone-dependent Dunning R3327 H tumour was strongly inhibited by zindoxifene (4 mg/kg), which was more effective than tamoxifen (43% T/C vs 87% T/C, the ratios of tumour weights in control and drug-treated rats). Zindoxifene was able to delay the relapse of these tumours by 7 weeks in comparison to castration. The experiments with Noble Nb-R prostatic tumours showed that administration of zindoxifene (5 mg) is superior to castration (5% T/C vs 52% T/C). The growth of tumours in castrated rats was completely inhibited by administration of zindoxifene. Therefore a peripheral mode of action has to be assumed.

Growth hormone receptor expression in the Dunning R 3327 prostatic carcinoma of the rat

The Dunning R3327 rat carcinoma is an important model for human prostate adenocarcinoma. In the present study this tumor was further characterized by immunohistochemical demonstration of receptors for growth hormone (GH-R). Weak GH-R immunoreactivity was present in the secretory epithelial cells of the tumor acini. Large epithelial cells which were localized at the periphery of the acini and large cells in the stroma, which are probably derived from the epithelium ("Large neoplastic epithelial cells"), displayed a strong staining with one of the monoclonal antibodies (Mab 263) to GH-R. The presence of GH-R receptors in proliferating prostatic tumor cells supports the concept that GH reacts directly on prostate target tissue to facilitate tumor cell growth.

Expression of endogenous receptors for neoglycoproteins in Dunning R3327 rat prostatic carcinoma

An important animal model for human prostatic adenocarcinoma is the Dunning R3327 rat carcinoma. In the present study this tumor was further characterized by analyzing the expression of endogenous sugar-binding proteins using glycohistochemistry and immunocytochemistry as well as affinity chromatography and gel electrophoresis. Our glycohistochemical and glycobiochemical results provide evidence for the presence of specific receptors for various carbohydrate moieties. Remarkably, basal cells of the Dunning tumor contain an endogenous lectin with specificity for beta-galactosides that is not found in basal cells of the normal rat prostate. This finding was corroborated using polyclonal antibodies against an immunologically related beta-galactoside-specific lectin from bovine heart. Basal cells of prostatic carcinoma may therefore behave different from normal basal cells. This difference could have a significant impact on the development of prostatic cancer.