2-Substituted estra-1,3,5(10)-trienes as anti-cancer agents: D-ring SAR and in vivo activity

A282 2-Substituted estradiol-3- O -sulfamates (E2MATEs) and 3,17- O,O - bis -sulfamates (E2bisMATEs) are potent anti-angiogenic and anti-proliferative agents which are differentiated from the corresponding estradiol derivatives by their superior activity and oral bioavailability. The ability of these molecules to inhibit the Taxol promoted polymerisation of tubulin underlies their pro-apoptotic effects:- G 2 M cell cycle arrest, p53 induction, BCL-2 phosphorylation and activation of various caspases are all observed in cancer cells treated with these compounds. Sequestration by red blood cells, through a reversible interaction of the sulfamate group with carbonic anhydrase, combined with the blockage of both deleterious conjugation and 17β-HSD II metabolism by C-17 substitution likely confer high oral bioavailability. Modification at C-17 of the D-ring ( e.g. incorporation of a 17- O -sulfamate group) has provided for enhanced activity, with SAR studies indicating that H-bond acceptor ability of the C-17-substituent is requisite for activity.
 A series of compounds was elaborated to further interrogate the C-17 SAR in the hope of discovering compounds with higher activity against the proliferation of DU-145 prostate cancer cells than the E2bisMATEs 1 & 2 (GI 50 340 & 210 nM respectively). Various H-bond acceptors were thus linked to C-17 via carbon linkers. Of the two-carbon linked H-bond acceptors in the 2-methoxy-3- O -sulfamate series, ketone 3 (GI 50 89 nM) proved especially active, with good activity also observed for the corresponding secondary alcohol (143 nM). Larger H-bond acceptors and non-sulfamoylated compounds displayed significantly reduced activity. Abbreviation of the linker to a single carbon afforded numerous novel compounds with activities in the low nanomolar range amongst which the 17β-acyl compounds proved particularly noteworthy. 2-Methoxy-17β-acyl-estra-1,3,5(10)-trien-3-ol 4 with a GI 50 300 nM is 4-fold more active against DU-145 proliferation than the clinical agent 2-MeOE2, thus emphasising the likely importance of interactions around C-17. The 3- O -sulfamoylated 2-ethyl- and 2-methoxy- 17β-acyl compounds 5 & 6 were exceptionally potent (GI 50 ’s 62 and 46 nM respectively), with alcohol and ether derivatives also displaying excellent activity. Thus, a number of novel, highly active, anti-proliferative agents were discovered by varying both H-bond acceptor group and C-17-alkyl linker to fine tune activity.
 Translation of this in vitro activity to the in vivo context was studied in a mouse Matrigel model of angiogenesis in which 3 and 5 were evaluated at 20mg/kg/day p.o. for 4 days. Results obtained confirm the in vivo anti-angiogenic effects of these molecules and the oral bioavailability that they display and justify further development of this general compound class.