Influence of derivatisation of the hydroxy groups in 1,1-bis-(4-hydroxyphenyl)-2-phenylbut-1-ene on estradiol receptor affinity and mammary tumor inhibiting properties

Investigations on the influence of terminal groups at the C2-propyl side chain of 1,1-bis(4-hydroxyphenyl)-2-phenylpent-1-ene and 1,1,2-tris(4-hydroxyphenyl)pent-1-ene on the estrogen receptor binding and the estrogenic/anti-estrogenic properties

1,1-bis(4-Hydroxyphenyl)-2-phenylpent-1-ene (5) and 1,1,2-tris(4-hydroxyphenyl)pent-1-ene (6) derivatives with terminal CN (5a, 6a), NH(2) (5b, 6b), NHCOCH(3) (5c, 6c), NHCOC(2)H(5) (5d, 6d) groups at the C2-propyl chain were synthesized and assayed in vitro for estrogen receptor (ER) binding affinity (RBA) in a competition experiment with [3H]estradiol and for estrogenic and anti-estrogenic properties in a luciferase assay with ER-positive MCF-7-2a cells, stably transfected with the plasmid ERE(wtc)luc. The CN as well as the NH(2) group reduced the RBA-values (5: 2.09%; 5a: 1.50%; 5b: 0.07%; 6: 4.03%; 6a: 0.67%; 6b: 0.20%) and the antagonistic potency (5: IC(50)=0.05 microM; 5a: IC(50)=0.43 microM; 5b: IC(50)=1.50 microM; 6: IC(50)=0.07 microM; 6a: IC(50)=0.60 microM; 6b: IC(50)=2.00 microM). Derivatization of the amino function with acetic anhydride and propionic anhydride did not change the RBA-value but altered the antagonistic profile (5c: IC(50)=2.50 microM; 5d: IC(50)=not detectable; 6c: IC(50)=0.65 microM; 6d: IC(50)=1.00 microM). Agonistic effects were only detected for the amine 6b (34.2% activation of the luciferase expression). These data document that estrogen receptor binding and the antagonistic effects can be modified by terminal groups at the C2-propyl chain of the pure antagonists 5 and 6. The mode of action is unclear. However, it can be assumed that the elongation of the side chain causes a reorientation in the LBD in order to locate the side chain in a side pocket near the ligand binding domain.

Investigations on estrogen receptor binding. The estrogenic, antiestrogenic, and cytotoxic properties of C2-alkyl-substituted 1,1-bis(4-hydroxyphenyl)-2-phenylethenes

C2-Alkyl-substituted 1,1-bis(4-hydroxyphenyl)-2-phenylethenes were synthesized and assayed for estrogen receptor binding in a competition experiment with radiolabeled estradiol ([3H]-E2) using calf uterine cytosol. The relative binding affinity decreased with the length of the side chain R = H (3a: 35.2%) > Me (3b: 32.1%) > Et (3c: 6.20%) approximately CH2CF3 (3d: 5.95%) > n-Pr (3e: 2.09%) > Bu (3f: 0.62%). Agonistic and antagonistic effects were evaluated in the luciferase assay with MCF-7-2a cells stably transfected with the plasmid ERE(wtc)luc. All compounds showed high antiestrogenic activity without significant agonistic potency. The comparison of the IC(50) values for the inhibition of E2 (1 nM) documented the dependence of the antagonistic effects on the kind of the side chain: 3a (IC50 = 150 nM), 3b (IC50 = 30 nM), and 3f (IC50 = 500 nM) were weak antagonists, while 3c (IC50 = 15 nM), 3d (IC50 = 9 nM), and 3e (IC50 = 50 nM) were full antiestrogens and antagonized the effect of E2 completely. The most active compound 3d possessed the same antagonistic potency as 4-hydroxytamoxifen (4OHT: IC50= 7 nM) without bearing a basic side chain. 3d as well as all other 1,1-bis(4-hydroxyphenyl)-2-phenylalkenes were not able to influence the proliferation of hormone dependent MCF-7 cells despite the antagonistic mode of action. In this assay tamoxifen (TAM) and 4OHT reduced the cell growth concentration dependent up to T/C(corr) = 15% and 25%, respectively.

1-[4-(N,N-bis-beta-chloroethylcarbamoyloxy)-phenyl]-1,2-bis- (hydroxyphenyl)-but-1-enes: drugs specifically targeted against estrogen receptor positive mammary tumors

1-[4-N,N-bis-2-chloroethylcarbamoyloxy)-phenyl]-1-(4-hydroxyphenyl )-2- phenylbut-1-ene (1) is a cytotoxic estrogen with a selective antitumor effect only on estrogen receptor (ER) containing tumors. In order to improve the ER affinity and thereby the antitumor activity of 1 a second OH-group in position 3 or 4 was introduced into the phenyl ring at C-atom 2 (8 and 9) and the respective acetates 10 and 11 were prepared. These modifications caused an enhanced ER affinity of 8-11 as compared to 1. The estrogenic properties were only slightly increased. In vitro, an enhanced antitumor effect on the ER positive MCF-7 mammary tumor cell line was determined for 8-11 as compared to 1 leading to inhibitions up to 90%. In vivo, 8-11 caused a pronounced growth inhibition of the hormone-dependent MXT M3.2 mammary tumor of the mouse though these effects were not better than those caused by 1 except the acetate 10, which inhibited tumor growth by 88%. These data show that the introduction of a second OH-group into 1 not only increased ER affinity, but also the antitumor activity in vitro and to a lesser extent in vivo in ER positive tumors. As none of these compounds had any significant effect on ER negative tumor models, 8-11 can be regarded as cytotoxic estrogens with a specific ER-mediated effect selectively on ER positive tumors.

Cytotoxic ester derivatives of the mammary tumor inhibiting antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane

The synthesis of the bis-acrylate 12, the bis-beta-chloropropionate 13 and the bis-beta-bromopropionate 14 of the "partial" antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane (7) is described. In the case of 13 and 14 the introduction of the beta-haloester-functions moderately reduces the estrogen receptor affinity of 7. However, it was quite strongly diminished in 12. The hydrolytic stability under in vitro-receptor-assay conditions decreases in the order 12 greater than 14 greater than 13. Compared with 7 the estrogenic potency of 12-14 is increased to a great extent. The title compounds cause a strong inhibition of the hormone-dependent MXT-M3.2 mouse mammary tumor.

Ester derivatives of the mammary-tumor-inhibiting antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane

The synthesis of the bisacetate (8), the bisdichloroacetate (9), the biscarbamate (10) and the bisphosphate (11) of the "partial" antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane (7) is described. In the case of 8-10 the introduction of ester functions slightly reduces the estrogen receptor affinity of 7. However, it was strongly diminished in 11. Compared with 7 the estrogenic potency of 8-11 is moderately increased. Compounds 8-11 cause a strong inhibition of the hormone-dependent MXT M3.2 mouse mammary tumor. Only 9 containing cytotoxic dichloroacetate groups shows a significantly better antitumor effect than 7.