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.

[N-ethyl- and [N,N'-diethyl-1,2-bis(2,6-difluoro-3-hydroxyphenyl)-ethylenediamine]dichloroplatinum(II): structure and cytotoxic/estrogenic activity in breast cancer cells.

N-Ethyl and N,N'-diethyl derivatives (erythro- and threo-2-PtCl2; meso- and D,L-3-PtCl2) of [meso- and [D,L-1,2-bis(2,6-difluoro-3-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (meso- and D,L-1-PtCl2) were synthesized and tested for cytotoxicity on the estrogen receptor-positive (ER+) human MCF-7 breast cancer cell line. In this test, only D,L-1-PtCl2 and threo-2-PtCl2 showed strong cytotoxic properties. This revealed the existence of at least one NH2 fragment as a prerequisite for antitumor activity. Furthermore, studies on the three-dimensional structure of the new compounds demonstrated that the aryl and alkyl residues at the five-membered chelate ring have to be arranged in equatorial positions for the triggering of cytotoxic effects, very likely due to the reaction with d(GpG) sequences in DNA resulting in GG-N7,N7 chelates. A contribution of the ER-mediated processes--(a) hindrance of the cellular processing of Pt-modified DNA by overexpression of high mobility group domain proteins and (b) interruption of the vicious circle of mutual growth stimulation of breast cancer cells and granulocytes/macrophages by reduction of the formation of key cytokines--to the anti-breast cancer activity of threo-2-PtCl2 is unlikely, since we did not observe transcription activation in the test on ER+ MCF-7 breast cancer cells stably transfected with luciferase reporter plasmid ERE(wtc)luc.

[1, 2-Bis(2, 6-difluoro-3-hydroxyphenyl)ethylene-diamine]platinum(II) complexes, compounds for the endocrine therapy of breast cancer - mode of action II: contribution of drug inactivation, cellular drug uptake and sterical factors in the drug-target interaction to the antitumor activity.

The marked activity of [meso-1, 2-bis(2, 6-difluoro-3-hydroxyphenyl)ethylenediamine]platinum(II) (meso-3-PtLL', L, L' = Cl(2) or L = OH(2), L' = OSO(3)) on the hormone-sensitive MXT-M-3, 2 breast cancer implanted in mice is most probably due to a mechanism based on the reduction of the endogenous estrogen level. Cytotoxic effects which are poorly pronounced in experiments on several breast cancer cell lines (e.g. MCF-7), do not significantly contribute to the anti-breast cancer activity of this compound. In contrast to this, the standard cisplatin and the structurally related comparison compound [meso-1, 2-bis(4-fluorophenyl)ethylenediamine]platinum(II) (meso-4-PtLL', L, L' = Cl(2) or L = OH(2), L' = OSO(3)) are strongly active in vivo as well as in vitro. Both effects entail programmed cell death, which is responsible for the inhibition of the tumor growth. The minor cytotoxicity of meso-3-PtLL' in breast cancer cell cultures is caused neither by an inappropriate rate of reaction with bionucleophiles (e.g. by a too fast inactivation by plasma proteins) nor solely by the observed poor absorption by the tumor cells resulting in an insufficient drug concentration at the DNA. Additionally, an impeded reaction with biologically important, guanine-rich sequences of DNA (owing to the 2, 6-standing F atoms which hinder the drug-target inter action) must be assumed as cause of its marginal cytotoxicity.

[1, 2-Bis(2, 6-difluoro-3-hydroxyphenyl)ethylene-diamine]platinum(II) complexes, compounds for the endocrine therapy of breast cancer - mode of action I: antitumor activity due to the reduction of the endogenous estrogen level.

Aqua[meso-1, 2-bis(2, 6-difluoro-3-hydroxyphenyl)ethylenediamine]sulfatoplatinum(II) (meso-3-PtSO(4)) and its racemate (rac-3-PtSO(4)) are highly active on the hormone-sensitive MXT-M-3, 2 breast cancer of the mouse. In vitro, on the MXT(+) cell culture derived from this tumor, however, they are inactive (meso-3-PtSO(4)) or moderately active (rac-3-PtSO(4)) in concentrations corresponding to levels of these drugs in animal experiments. The in vivo effect is mainly caused by a reduction of the endogenous estrogen level in the host animals due to an interference with the ovarian steroid biosynthesis as demonstrated for meso-3-PtSO(4). Therefore, a reversal of the breast cancer inhibiting effect of meso-3-PtSO(4) can be achieved by simultaneous estrone administration. Histological results on ovaries, uterus, and tumor of meso-3-PtSO(4)-treated mice also favor such a mode of action. However, especially for rac-3-PtSO(4) cytotoxic effects contributing to the anti-breast cancer activity cannot be excluded. Considerations on the mode of action of Pt-complexes which inhibit breast cancer by interference with estrogen receptor mediated processes of growth control and with DNA replication are presented.

Establishment and characterization of new murine breast cancer cell lines.

The establishment of two new breast cancer cell lines, MXT+ and MXT-, derived from the murine breast cancer models MXT-M-3,2 MC (hormone-sensitive) and MXT-M-3,2 (ovex) MC (hormone-insensitive), is described. Characterization of the cell lines was performed by investigation of morphology, steroid hormone receptor state, growth kinetics, and drug response as well as by cytogenetic analysis. MXT+ contains estrogen receptors (ER; 6.9 fmol/mg protein) as well as progesterone receptors (PgR; 9.2 fmol/mg protein) and therefore is inhibited by tamoxifen (Tam). MXT- proved to be ER- but PgR+ (23.4 fmol/mg protein) and, as expected, resistant against Tam. The sensitivity of MXT+ and MXT- against a pattern of therapeutically established anti-breast cancer drugs (cDDP, cisplatin; JM-8, carboplatin; DX, adriamycin; 5-FU, 5-fluorouracil; MTX, methotrexate; VLB vinblastine) was studied by use of a computerized, kinetic chemosensitivity assay based on quantification of biomass by staining cells with crystal violet. For each compound the inhibition profile reflecting cytostatic, transient cytotoxic, or cytocidal drug effects as well as development of resistance was evaluated. The following order of activity was found: MTX > VLB > or = DX > cDDP > or = 5-FU > JM-8. The test data of 5-FU, VLB, cDDP, and Tam on MXT+ as well as on MXT- were compared with those from studies on ER+ and ER- human breast cancer cell lines (MCF-7, ZR-75-1, T-47-D, and MDA-MB-231, respectively). They revealed comparable inhibition profiles and sensitivities of human and murine breast cancer cell lines, an indication that the results achieved in combined in vitro-/in vivo tests by use of the murine test models MXT+, MXT-, MXT-M-3,2 MC, and MXT-M-3,2(ovex) MC are relevant for therapy in humans.

Establishment and Characterization of New Murine Breast Cancer Cell Lines.

The establishment of two new breast cancer cell lines, MXT(+) and MXT(-), derived from the murine breast cancer models MXT-M-3, 2 MC (hormone-sensitive) and MXT-M-3, 2 (ovex) MC (hormone-insensitive), is described. Characterization of the cell lines was performed by investigation of morphology, steroid hormone receptor state, growth kinetics, and drug response as well as by cytogenetic analysis. MXT(+) contains estrogen receptors (ER; 6.9 fmol/mg protein) as well as progesterone receptors (PgR; 9.2 fmol/mg protein) and therefore is inhibited by tamoxifen (Tam). MXT(-) proved to be ER(-) but PgR(+) (23.4 fmol/mg protein) and, as expected, resistant against Tam.The sensitivity of MXT(+) and MXT(-) against a pattern of therapeutically established anti-breast cancer drugs (cDDP, cisplatin; JM-8, carboplatin; DX, adriamycin; 5-FU, 5-fluorouracil; MTX, methotrexate; VLB vinblastine) was studied by use of a computerized, kinetic chemosensitivity assay based on quantification of biomass by staining cells with crystal violet. For each compound the inhibition profile reflecting cytostatic, transient cytotoxic, or cytocidal drug effects as well as development of resistance was evaluated. The following order of activity was found: MTX >, VLB >/= DX > cDDP >/= 5-FU > JM-8. The test data of 5-FU, VLB, cDDP, and Tam on MXT(+) as well as on MXT(-) were compared with those from studies on ER(+) and ER(-) human breast cancer cell lines (MCF-7, ZR-75-1, T-47-D, and MDA-MB-231, respectively). They revealed comparable inhibition profiles and sensitivities of human and murine breast cancer cell lines, an indication that the results achieved in combined in vitro-/in vivo tests by use of the murine test models MXT(+), MXT(-), MXT-M-3, 2 MC, and MXT-M-3, 2(ovex) MC are relevant for therapy in humans.