[Aqua-1-(2,6-dichloro-4-hydroxyphenyl)-2-phenylethylenediamine] sulfatoplatinum(II) complexes with variable substituents in the 2-phenyl ring. 3. Investigation of breast cancer inhibiting properties.

In the search for new anti-breast cancer compounds a series of diastereomeric aqua[1-(2,6-dichloro-4-hydroxyphenyl)-2-phenylethylenediamine]sulfato platinum(II) complexes was tested on the hormone-sensitive MXT-M-3.2 breast cancer of the mouse. By simultaneous determination of tumor and uterine weights at the end of the experiment we obtained an insight into the mode of action. Changes in the uterine weights indicate whether the anti-breast cancer effect of the test substance is caused either by its capability to reduce the endogenous estrogen level via inhibition of estrogen biosynthesis (mechanism B), or by its estrogenic side effects which enhance the immune defense in the host animals (mechanism C). Studies on the [3H]thymidine incorporation into DNA of MDAMB-231 breast cancer cells showed that all test compounds inhibit deoxyribonucleic acid synthesis, like cisplatin (mechanism A). However, in comparison to the standard cisplatin, their activities were low. The three most effective test compounds threo-2-PtSO4 (2-phenyl-residue), threo-5-PtSO4 (2-(4-hydroxyphenyl)-residue), and threo-8-PtSO4 (2-(2-fluoro-4-hydroxyphenyl)-residue) seem to exert their anti-breast cancer effect by mechanism B. Moreover, threo-5-PtSO4 was moderately active on the hormone- insensitive MXT-M-3.2 (Ovex) breast cancer of the mouse. Aqua[erythro-1-(2,6-dichloro-4-hydroxyphenyl)-2-(2-chloro-4-hydroxypheny l) ethylenediamine]sulfato-platinum(II) (erythro-9-PtSO4) was the only breast cancer inhibiting compound of the series acting mainly according to mechanism C. A minor contribution of mechanism A, impairment of the DNA function in the tumor cell, to the anti-breast cancer activity of these aqua[1-(2,6-dichloro-4-hydroxyphenyl)-2-phenylethylenediamine]sulfato platinum(II) complexes cannot be excluded, since such effects are apparent in the MDA-MB-231 as well as in the MCF-7 breast cancer cell line at higher drug concentrations. In this test series which was performed with the crystal violet chemosensitivity assay, the MCF-7 cells proved to be somewhat more sensitive.